[NoOne]

~30-35 isn't too many at all. you need that many capable of playing at that level to cover injuries.

it is a dropdown box. League Settings - then one of the sub-tabs... i think "stats and ai" has it.

you'll have to read the screen to know exactly what to change. rotation size at top, # of bench or rp then the 'one' without a setting is deduced/controleld by the other 2 options etc... i don't have perfect recall on that particular screen. (# of sp/rp/bench)

if you control depth charts, i'd toss the worst prospects at bottom of pen to minimize use and maximize time of better prospects (avoid overuse, of course)

belated edit:

if you meant roster rules -- league settings->rules, then select league. can set roster max, age/svc time max etc per league. since you specifically want RP help, the stats and ai settings are probably a better way.