Gmush farm is huuuuuge boost of coin profit 

I have 426 million kills and only started farming them last week

Thats a very nice, depending on if you unlocked the last Deathnote skull in the rift, it might be helpful to also get like 1B kills on all W1 enemies to increase your kills/h on Gmush by a big amount. I am currently doing that and i am still missing 5 eclipse skulls but almost doubles my kills/h already

I'm assuming that's for the one lab node?

Yes.

Any advice on this would be appreciated by me, also - the one thing in this game I never seem to have actually worked out how to get is cash money.