If I remember correctly, yahoo used 3SP, 2RP, and 3P. Let's assume that 2 of the bench spots will be used up for additional starters. Let's also assume that this will leave the average player with 5 starters, 2 middle relievers, and 3 closers. I would allow 1050-1100 innings for the 5 starters, 160-180 for the 2 mids, and 190-220 for the 3 closers. This would give you a range between 1400-1500 innings total, which is what I would recommend. If you think the average players would end up using 6 starters and only 2 closers instead, I would adjust the innings limit by about 100-120. Hope this helps.
Please take a look at my post "Opinions on this draft pick trade please."