i had my license a while ago and here is my experience with what you are asking
-training and courses : there will be set times you need to show up at some of the training sessions. if you have another job, it may interfere
-solid mentor - that means shared commission - at one brokerage, you will have to share half your commission with the mentor for your first 2 houses. and no, you don't trail behind the mentor on their deals--they assist you on your deals.
-nowadays, they have a transaction coordinator, who keeps tracks of the deals' progress, which helps in closing deals. there is a charge for that if you decide to have someone else monitor the progress of the deal.
-some don't charge desk cost, but require high commission paid to brokerage; some charge desk cost, with lower commission to brokerage.
-if you want 80/20, it may be best to look for one that has desk cost; some brokerage also have tiered system, that 80/20 split is only achieved if you reach a certain level of commission.
here's is my take on it -
deals are relatively hard to find and training materials are easy and you can even resort to a transaction coordinator if you need one, i would go for a brokerage that doesn't require a mentor, unless they don't require a commission split and have a favorable commission split to you.
i.e. a typical california house 500 K
commission is 6% = 30,000.
80/20 split = 24000 to you
if you have mentor that requires 50:50, then that's 12000 gone. (you can do the calc yourself for your actual situation)
you will realize that 12,000 probably took only a few hours total of mentor's time in the whole transaction, while you were doing all the footwork either as listing or buyer's agent. most of the information is already in the study materials you've had--the nuances can be learned from you actually going out there; even if they spent 24 hours total on you, you're paying them 500/hr.
of course, it's ultimately down to the details.