drdante on 18 July 2015
I have 8 GB memory cards and its enough for me. You can transfer your games (digital, save data, etc) to your PC as a storage and delete them in your Vita once the transfer is completed. That is what I did because I don't have enough money to buy larger memory cards and most of the money I spend on buying games. Its quite pain because you can't cut and paste into the PC but no biggie.
As for Borderlands 2, the game is great on Vita and played smoothly after the patch. You just need to download the update (it'll come out automatically after installed) and you are good to go.
Most of your questions have been answered from the above posts so I'm gonna leave it there 
