Lewis has the ability to be very consistent, he is probably the fastest driver in F1. Button is nothing to worry about, Lewis will be nr 1 in that team.
Alonso in a Ferrai will be very interesting, if Ferrai give him a good car then he has the talent to win, he won 2 world titles in a Reanult beating Schumacher into retirement in the process.
Brawn had a very poor end to the season, in fact they had a very poor second half of the season, it wil all boil down to the car they can give Schumacher. Ross will be pulling out all the stops to give him what he needs, if he can do that they he will be fighting it out with Hamilton & Alonso, Vettel will be in the mix also.
Mclaren & Ferrai had a poor season last season and they will have started developing this seasons car much much earlier than Brawn will have and as a result will have an advantage imo. Ferrai will also not want to be beaten by Brawn/Schumacher. Ferrai have also just completed building and revealed the worlds most advanced race simulator which will be of great use with the limited number of tests (it took 2 years to build).
Overall, next season will be so interesting on so many fronts, I think it will be amazing, I hope Schumacher does win the world championship for an 8th time but I can see a 3/4 way battle against the big teams with ever point counting so he better get off to a flying start