A lot of good suggestions so far.
2017 was there 3 times on a 12u team, once each in 2010, 2011 and 2012. Mom had enough of Cooperstown after the 2nd year, but my son has a lot of great memories. In his final year he won the HR Derby. In 2011 and 2012 they made it to the round of 16, but a lack of pitching depth did us in.
Use your best pitchers early in the week as you'll need them again on Wednesday and Thursday.
Shoot for no less than 4-2. Anything worse than that and you're playing too many games on Wednesday. However, no matter where you finish, you'll play too many games. 
Best case scenario you'll play 11 games in 5 days.
Pitching depth is a must. When teams are tied with wins and losses, which they will be, runs against come into play.
Many teams scout their upcoming opponents. I suggest you do the same.
The extra hitter, if you're batting 10, must hit last in the order.
Work on the skills competition events at practices for about two weeks before you go. Depending on your team, it may be the only trophy your kids leave with.
I still have a "Cooperstown Survival Guide" for coaches, parents and players, that is 7 pages of pretty good info. I could email it to you if you like.
Above all else... enjoy the week. It's definitely one of the best weeks that 12 year olds will have. They will have a lot of fun memories.