The PlayStation Plus Edition of DriveClub will give you access to all of the game's features offline and online according to Game Director, Paul Rustchynsky.
Speaking in response to a user question on the PS Blog, Rustchynsky said that the only difference between the full version and the PlayStation Plus version is that in the latter you'll only have access to 10 cars and you can only race in one country (which gives you access to 5 tracks with 11 distinct variants).
You'll still have access to the main social features of the game and if you enjoy what you're playing then you can upgrade from the PlayStation Plus version to the full version for a set cost.
You could of course just buy the game from ShopTo. But whatever you option you choose, DriveClub is looking rather nice.