I'm relatively new to keeper leagues but I would follow the following guidelines.
$260 auction budget
$350 in season cap
23 active players (2 C, 1B, 2B, 3B, SS, MI, CI, 5 OF, U, 9 P
5 bench spots
I would play the normal 5x5 roto or if you want to change it up a little bit switch out AVG for OBP. Getting other things involved really turns things wacky.
Depending on the # of teams you have will determine keepers per team. If its a 15 team league I would say you can keep anywhere up to 8 players.
You will also need some sort of salary increasing system for keepers (for ex. salary for every player you keep increases by $2, $3, etc.)