The idea of having a junior adventurer go out and help with stuff that's great cool I get it.
The fact I have to waste an inventory slot and farm tokens for something that has an extensive time cooldown anyway?
Not so much.
This system is very time intensive.
1) Farming for ventures involves either alot of hunt or Grand Company or leave grinding. Not fun.
2) To be "optimal" one has to be logged in 24/7. Yes there are long ventures, but you get one "roll" vs ?12? and the odds don't seem to be better for the longer ventures.
3) It's near impossible to have all 4 retainers out constantly and not run out of ventures.

Idea:
Remove the venture token.
Allow adventures to pay retainers in Gil.
Or better yet, just remove the cost and stick with the time / upkeep cost.
Other option: make ventures tradable.