I've never played these games before, and I'm new to following basketball, If i buy this game does it come with the full nba rosters? ie curry at the warriors or do I need to download it seperate>? if i need to download it seperate then how?

The game isn't licensed by the NBA, so the answer is technically no. That said, I'd recommend downloading the demo and checking the rosters and see how they work for you.

The community also does a great job creating mods that are realistic in scope and detail, which you can find here: viewforum.php?f=342