Personally, I think 1800 innings is ideal for pitching. By doing 1800 innings, you make pitchers and hitters closer to the same value per inning played. If you do 1250, a single pitcher could account for 1/5 to 1/6 of all of your innings, when a hitter will only account for 1/9 of the total innings. If you did 1250, someone like Santana would be the most valuable player in the league, whereas if you did 1800, he would barely be a first round pick.
I would say that in Roto you should have a MINIMUM of innings pitched. Only having a maximum could lead to people staffing MR and winning ERA and WHIP. Have a free agent acquisition budget, this way they can't be adding and droping pitchers everyday and rackup in SO and W but his ERA and WHIP will go the opposite way.
What positional players is up to you as this will determine the depth of your league.
I play 12 team NL Only, 23 positional players(14b & 9p) with no bench.
You should join a couple of free yahoo leagues and see what you like best.
I am a fan of player aquisition limit to prevent people from streaming
max innings does the same thing for pitchers but you can stream a lot of hitters in leagues just as bad if you dont click the maximum games limit as well (to prevent people from loading up on those short Mondays and Thursdays)
one league im in has an interesting rule but its a PAIN for commish to watch 1 pitcher per day so people cant hoard pitchers
1250 innings are enough. in one of my 15 team roto leagues 9 pitchers, i ran 27 different pitchers in and out of my lineups and totaled 1342 innings, and scored 48 out of 60 points (4x4). 1250 is enough for most leagues.