SDHC = SD High Capacity

aware of~
class number, class 10 gives out the best minimum read/write speed useful if you frequently transfer large files in and out of your phone with your computer. But for usual we recommend class 4 or class 6, i'm personally using class 4 sandisk and i dont find any problems, althought i would recommend class 6.

aware of fakes
some written class 4/6 but actually is class 2
some written 32GB but actually is 16GB (the capacity will write 32GB even in computer but when you transfer files and fill up the sdcard more than 16GB, the extra files will get corrupted)
some sdcard are actually china products.

unfortunately i cant teach you how to know they're real or fakes, you can google or look around in the lowyat forum to know.

Sdcards requires FAT32 format, so anything more than 4GB cant be put inside. But if you're rooted, you can put in a NTFS format sdcard after copying some files and running some commands, which supports files more than 4GB

32GB is not the limit, so far i dont think there's a limit to the sdcard size, it is proven even 64GB sdcard will work if formatted to FAT32