how many maps will there be at launch?

[–]We are still finalizing it as we test different times of day/ weather effects. But it will be somewhere between 5 and 7. And all other arenas that we have post-release will ALWAYS be free. You will never pay for a new Arena/ Stadium in Rocket League. Ever.
...Other DLC, on the other hand, we will most likely charge for.
 
Can you tell us what kind of DLC will be paid? I guess customization and maybe cars right? I'm totally ok with that.

[–]We can't yet because we're still figuring it out. We were thinking of working on DLC the second (literally) that we get Rocket League submitted and out the door to get it as close to launch as possible. What that will be -- whether it would be a Free Arena or a paid something else, we're still figuring out.
Off the top of our heads, though. The most immediate, most likely things would be stuff like new cars or decals or paint types or other customization items that would add to the personalization aspect of the game.
 
Are you thinking of doing a season pass? I mean, I want all the DLC in one go already, just to support even more this awesome game.

[–]In regards to a season pass, anything is on the table right now. We haven't ruled anything out.
The only DLC thing we know for sure is that Arenas will always be free and will be included as patches and not store downloads.
(and thanks!)