In my opinion, with Milan's full-backs you won't be playing very well. You need to buy better ones ASAP.
The rest of the team seems all right, although both Ronaldinho and Seedorf are going to be "tired" constantly...
I don't know how this tactic will work because it was kind of assymetric, but not sure how this affects the game... But here are a few hints:
1) The place you put Ronaldinho is where he plays in real life. However, in this game he works much better as a central attacking midfielder. That's the position he's natural at. It's the only position I have managed to see him get a 7+ rating after a whole season...
2) Maybe try a 4-3-3 or 4-4-2 Diamond, might work better. IT's what I used for the first seasons and worked quite well, even before I bought better players... leave a good DM behind (Gattuso or Ambrosini), put Ronaldinho as a AMC and two midfielders to support... Pirlo should be on the team, the other you can decide/rotate. My 4-3-1-2 (no DMC, leaving 3 MCs one of them with defense duties) worked even better than the 442 Diamond, but it depends on how your team settings are defined...
Also, have a look at this thread. I put some of the questions I have and how my new tactics is. With a few reinforcements, it will work for you too I hope. I also mention a "tweaked" tactic that wins everything.. you can get some inspiration from there..
Hope I helped...
http://www.fm-base.co.uk/forum/f72/ac-milan-tatics-overall-instructions-t42108.html