Wow that sounds like a brutal league, only for the hardcore! If you guys are up to it great, otherwise, you probably should stick to 5X5 or 6X6.
With 27 spots times 16 teams, you have a whopping 432 players out of your player pool on rosters.
I'd cut 2 pitcher spots, and get rid of the CI and MI spots. That gives you 32 more pitchers and 32 more position players in the player pool.
16 teams is alot. Your shcedule is going to be a challenge. You will play every one in the league once and then 6 teams 1 more time, so how you setup your playoffs is going to be important. You might want to do a toilet bowl. You are going to have alot of teams out of contention which will skew your results in the second half.