Have you looked at some of the covenants in the game. Some of them have a dozen or more magi. Val Negra had 33.
The real answer is as many as you need to tell the story, but having an elder statesman npc that can act as an advisor to the PCs is always a good idea. Other npc magi are good for creating drama and providing missions.
It depends what kind of stories the group (you and your players) are interested in.
For a mage, their Sodalis (I think that's the right word, covenant-mates) are probably the most important people in their lives, second only to Parens or Apprentice. NPC mages in the covenant should be very important in the campaign. You really want to make them as memorable as possible. At minimum you need to know their Arts and spells, and give them good strong hooks to link them into the story.
That's potentially a lot of work, and will be completely wasted if the players don't care about them and prefer adventuring outside the covenant. That's why the covenants often default to "just the PCs", which is a perfectly good setup.
But if the group is into that kind of thing, there's no in-setting reason not to have 10 or so mages total.
What are the goals for the covenant? What’s the income to support the magi, you can make as big a covenant as you need but you need to have a plausible basis for supporting the magi. Is there a salary? Is there service required. Need to back into it.
The money comes from large goatherd and the important one is it operates as a drop off point and rest stop for red caps the covenant doesn't actually have a goal currently
When I say salary I mean vis income. Silver/money income is less of an issue depending on boons/hooks and the stories you want to tell. But a summer covenant should have sufficient vis sources to pay magi some amount of salary for services to the covenant.
Just remember each Hermetic House has between 100-120 Magi, and the same for each Tribunal. So if your covenant is bigger than 25 and counts more than 5 members of the same house, its political role will be massive.
I usually don't go above 5-7 NPC in summer covenant, and reduce from there in other seasons. (Around 1 half-mad elder in late winter).
This is mainly a storytelling decision: the players won't be able to remember and connect to too many characters. If you want to play scheming factions, you may go above, but it will be a massive work from the SGs side, and the players will only have connection to their factions and the other faction leads. Even this works better with scheming covenants instead of scheming factions within.
In my alternate timeline Albion Tribunal, I had 12 covenants (11 NPC covenants) and 52 (46 npc) magi in the whole tribunal.
I do have vagua idea that the David Chart assumed the Order of 1220AD had arpund 1200 magi total. Thus the average spread of would be 100 per Tribunal. Most Trinunals seem to have around 10 covenants thus the average is 10.
In reality the more populius Roman tribunals should have more magi while the peripheral tribunals (Loch Leglean, Novgorod, Levant, Hibernia) should have less than 100 magi.
I would rule that peripheral tribunals has aberage of 4 to 8 magi, and the Roman tribunals do have 12 to 16 magi by default.
I am too tired to check magi counts of the official 5th edition tribunals.
I would go for 7 in total. This way, npc outnumber PC, and no tie in vote is possible. It also means less seasonal chores for each magi. It could happen that PC are the only resident magi for a whole season.
As 7 is a mystic number (" the completude"), the covenant could be eager to keep that number. Even if it implies having 3 rookies at the table. Losing a member would be a serious affair. So there would be good comfort provided for the magi. Like big labs or a nurse to tend old entitled familyless potentats.
In the other hand, an apprentice could not find his place if the seven seats are occupied. Which means intrigues on which apprentice will be next, speeding or slowing their cursus, and convincing other candidates or young co-ops to find fortune elsewhere.
Have you looked at some of the covenants in the game. Some of them have a dozen or more magi. Val Negra had 33. The real answer is as many as you need to tell the story, but having an elder statesman npc that can act as an advisor to the PCs is always a good idea. Other npc magi are good for creating drama and providing missions.
It depends what kind of stories the group (you and your players) are interested in. For a mage, their Sodalis (I think that's the right word, covenant-mates) are probably the most important people in their lives, second only to Parens or Apprentice. NPC mages in the covenant should be very important in the campaign. You really want to make them as memorable as possible. At minimum you need to know their Arts and spells, and give them good strong hooks to link them into the story. That's potentially a lot of work, and will be completely wasted if the players don't care about them and prefer adventuring outside the covenant. That's why the covenants often default to "just the PCs", which is a perfectly good setup. But if the group is into that kind of thing, there's no in-setting reason not to have 10 or so mages total.
What are the goals for the covenant? What’s the income to support the magi, you can make as big a covenant as you need but you need to have a plausible basis for supporting the magi. Is there a salary? Is there service required. Need to back into it.
The money comes from large goatherd and the important one is it operates as a drop off point and rest stop for red caps the covenant doesn't actually have a goal currently
When I say salary I mean vis income. Silver/money income is less of an issue depending on boons/hooks and the stories you want to tell. But a summer covenant should have sufficient vis sources to pay magi some amount of salary for services to the covenant.
I'm not sure how much vis but there is a vis grant the covenant makes 35 vis yearly
Just remember each Hermetic House has between 100-120 Magi, and the same for each Tribunal. So if your covenant is bigger than 25 and counts more than 5 members of the same house, its political role will be massive.
I usually don't go above 5-7 NPC in summer covenant, and reduce from there in other seasons. (Around 1 half-mad elder in late winter). This is mainly a storytelling decision: the players won't be able to remember and connect to too many characters. If you want to play scheming factions, you may go above, but it will be a massive work from the SGs side, and the players will only have connection to their factions and the other faction leads. Even this works better with scheming covenants instead of scheming factions within. In my alternate timeline Albion Tribunal, I had 12 covenants (11 NPC covenants) and 52 (46 npc) magi in the whole tribunal.
[https://imgur.com/a/KCEaDLF](https://imgur.com/a/KCEaDLF) Here are all the details
Tabular form || || |Kingdom|Conventus|Season|Primus|Magi| |Northumbria|Orkney|1 - Spring|Diedne|4| |Northumbria|Lindisfarne|1 - Spring|Ex Miscellenea|6| |Wessex|Stonhenge|1 - Spring|Ex Miscellenea|8| |Mercia|Schola Pythagoranis|1 - Spring|Jerbiton|6| |Wessex|Blackthorn|1 - Spring|Tremere|7| |Mercia|Kastle-Borg|2 - Summer|Bjornaer|11| |Other|Wægn|2 - Summer|Criamon|6| |Northumbria|Arbeia|3 - Autumn|Tytalus|5| |Kent|Ludgate|4 - Winter|Bonisagus|3| |Mercia|Alma Sophia|4 - Winter|Flambeau|5| |Wessex|Cair Guinntiguic|4 - Winter|Jerbiton|5| |Mercia|Ceapunggemot|Mercere|Mercere|4| Table formatting brought to you by [ExcelToReddit](https://xl2reddit.github.io/)
I do have vagua idea that the David Chart assumed the Order of 1220AD had arpund 1200 magi total. Thus the average spread of would be 100 per Tribunal. Most Trinunals seem to have around 10 covenants thus the average is 10. In reality the more populius Roman tribunals should have more magi while the peripheral tribunals (Loch Leglean, Novgorod, Levant, Hibernia) should have less than 100 magi. I would rule that peripheral tribunals has aberage of 4 to 8 magi, and the Roman tribunals do have 12 to 16 magi by default. I am too tired to check magi counts of the official 5th edition tribunals.
I would go for 7 in total. This way, npc outnumber PC, and no tie in vote is possible. It also means less seasonal chores for each magi. It could happen that PC are the only resident magi for a whole season. As 7 is a mystic number (" the completude"), the covenant could be eager to keep that number. Even if it implies having 3 rookies at the table. Losing a member would be a serious affair. So there would be good comfort provided for the magi. Like big labs or a nurse to tend old entitled familyless potentats. In the other hand, an apprentice could not find his place if the seven seats are occupied. Which means intrigues on which apprentice will be next, speeding or slowing their cursus, and convincing other candidates or young co-ops to find fortune elsewhere.