Not sure if this is the best way but it works for me. I grow them up in 10ml of wort (in a test tube) for 2 or 3 days and then streak some plates. I let them grow on there for a few days and then try to find 10 colonies that look like they started from single cells. I put those 10 colonies...
good paying job, stressful but pays well. Me too :) Many people (including my wife) asking why I want to give that up to be kicked in the nuts on a daily basis. For me, the well paying job isn't interesting anymore.
I sent you a message with links to pictures.
The starter is fine. The slant, like ba-brewer says, may be hard to work with if those bubbles hardened.
I usually put a few drops of Fermcap in to keep the bubbles away.
https://www.morebeer.com/search?search=fermcap
I'm guessing you are doing 38L (10 gallon) batches? I also think the cooler route would be a good one. The question is, is a 10 gallon cooler big enough...
I have never done BIAB but if I were in your shoes, I would probably be giving that some considerable thought. It seems like BIAB may be better for smaller batches though? I don't know. Anyway, I think you need some boil and mash capacity. I did many 10 gallon batches with a 15.5 gallon boil...