Vita newbie! Huzzah! Help please?

So my friend just sold me his PS Vita today for a good price. Got Persona 4 Golden and Hot Shots Golf and DJ Max Technika on the memory card. I've got a few questions since this didn't come with a box or manual and I'm hoping you good people could help me :D

My friend's PSN account is tied to the system, is there any chance I can delete his account and make one of my own? Also can I transfer his purchase of DJ Max to a new account?

If I can't transfer purchases, do you guys think it'll be a good idea to reformat and have my own account with my own data? I do plan on subscribing to PS+ and using this account on a possible PS4 in the future or would it be more practical to just keep his account and change data (if possible)?

I currently have a 4 GB memory card. Will that be good enough or would you guys recommend getting a bigger card? I plan on getting the games through retail but I might download PSone, PSP, and other PSN games in the future.

Lastly, what are the benefits of PS+? From what I gather, you get big discounts in the PSN store and free games each month? Or is there something more?

I highly appreciate anyone who will help this Sony newbie out :P Thanks! 

You can't transfer digital purchases, as it's exactly the point of PSN accounts and PS+. They enforce a marketing philosophy where you can't resell, lend, trade or give away for free a downloaded software, as you could do with a cartridge/disk game. Basically, you pay to play a game, but don't really "own" it.

If you plan to go with PS+, you'll want to reformat everything, without hesitation.

PS+ offer is 100% value oriented, so, yes, free stuff, discounts and gifts consisting in dollars/euro credited to your account.

If you plan to go with PS+, you'll want to reformat everything, without hesitation. rongxinge

What the heck, you just copy-pasted the first guy's reply?!!