did some searching

You get 250K if you buy season pass
Q. Why should I purchase the Forza Motorsport 4 Season Pass?
A. Purchasing the Season Pass gives you access to six 10-car packs at a 30% discount. Xbox Gold subscribers who purchase and redeem a Season Pass code in the first week of availability will also receive 250,000 in-game credits to be delivered through their game by Oct. 31, 2011 11:59PM PST. If that weren't enough, a Season Pass will also net you the American Muscle Car Pack for free!
profile import details at bottom
For those who have invested tireless hours in “Forza Motorsport 3”, Turn 10 Studios is pleased to announce a unique “Forza Motorsport 4” feature called Profile Import, which rewards fans for their time. Based on your player level and the cars in your garage in “Forza Motorsport 3”, gift cars will be automatically added to your “Forza Motorsport 4” garage and you’ll also receive bonus gifts and credits. And for those who spent hours creating intricate layers and liveries in the “Forza Motorsport 3” Livery Editor, you will be able to import those layers, so your time isn’t lost!
Pretty much answers most of the questions, click me

....really sucks that I accidentally deleted my game save (300+ cars, level 50, ~3 races left)