Hitched in Brazil and work permits

Oi, bonjea meu amigos

My girlfriend is Brasilian and she has been in the uk for 3 months on a visitors visa. In Sptember i'm look at both of us returning to Brazil. My question is when I return the most I can stay for is 90 days then an extention by the federal Police for a further 90 days.
We are looking at getting married during the 6 months and i'm sort of guessing that if we are married then I can apply to stay longer with my wife and I may be able to work - can somebody confirm this please....I also need to know if I can drive on a uk licence or how i can ontain a transfair to a Brasilian liceence...Many Many thanks
Tchau