I agree with the others: Don't change anything!
- The number of players will go down eventually. No worries. Just make clear that you absolutely do not accept new players now. Period.
- The wealth level will buff itself out. Just don't hand out any treasure for 2-3 levels, and it should be fine. Don't even announce it! It's just that the PCs happen to join this big war against the ultimate evil, out of sheer selflessness.
- Stats too high: Ah well, it happens. Just enforce point buy next time. Rolling for stats shouldn't have been in the game all the way back to the 70ies, but that's too late to change now. If it's 4E you're playing, you should be fine anyway as long as all PCs have their main attack stat in the same range.
In general, don't worry about running the game "by the book". Before you implement any changes on your side, just ask your players: Are you guys having fun? Don't change the game if the players are happy the way it is.
Oh, and don't bump the PCs five levels, have them earn each XP they get. If the game is too "easy" (no wonder, with 10 PCs your party is twice as strong as expected) throw harder monsters at them (not sure about just using more monsters, combats could take forever)