I would think you want something much bigger then 100BTC. If you look at Prime Dice's thread in the very first day someone won 200 BTC. I mean you can't expect te same thing but to plan for the worst. I would assume you would want 500 or more. Depends on what your max bet is going to be. If you use 1% of your BR as max bet and max bet is 5 BTC then 500 btc should be ok. Anything less and i think you may run into problems esp if you take off and have great success early.
It's hard to compare primedice with op's situation because bitcoin back then wasn't much expensive so bankroll isn't a big problem for them. Imo setting a max bet is not good because a bettor can simply set it on any multiplier and have a chance to win then the casino's bankroll is already destroyed, it's much better if he set it on max profit than max bet.
I do believe what he means by max bet is max profit per bet so it will not destroy the bankroll if OP use 1% of BR as max profit per bet. Of course anything may still happen if a lucky gambler win the max profit per bet continuesly in a row.
I think, OP can just start with what he have on his wallet. No need to force himself to provide so huge bankroll, let the bankroll increase by itself maybe by offering investment. Or he can simply use moneypot as the bankroll which will be safer for him.