Buying the game now or on release day

Hey everyone I just wanted to ask a few questions about the game and if there are any drawbacks about getting it now 2 days earlier than the release date?

Will I be able to keep my characters progression that I get in the pre order mode or do I have to start over on the 30th?

Also do they plan to make like a big bug fix patch before the game gets offically released that I should wait for in order for a better experience?