Need Micro SD card, what should I get? performance? Good place to buy one?

I picked up the Witstech A81E+ for my daughter:

Witstech A81E+ Gsensor Android 2.2,800MHz Market+Case+Bluetooth Removable battery

I need to get a card for it and I am thinking either a 16gb or 32gb card. How crucial is the classification of the card? I mean a class 2 vs. class 6 for these type of devices is going to effect the performance how?

I have seen on some other forums where they take a tablet apart and the internal storage is nothing but a card like I am asking about. They replace the card with a bigger and faster card. Is this model of tablet one i could do that with and is this something I should consider doing or not??

Lastly, anyone see any really good deals on cards??