Just to add to all this:
1) microSD and mircoSDHC are basically the same thing, but with different capacities. Newer cards with high data capacities like 16GB, 32GB are microSD HC (High Capacity). Unless you're dealing with old devices, they are compatible with any microSD card reader.
2) Class 4 and Class 10 cards differ in their read/write speeds. While a Class 10 is faster (and therefore more expensive), it all depends on what you intend to use the card for. Class 10 should be optimal for FullHD Video Recording but Class 4 is also capable of handling this, even if it's pushing it to the limit.
3) Samsung and SanDisk have a history of 'not liking each other'. I'd suggest you hang on to your purchase receipt and/or warranty card for a few months. Most SanDisk cards (unfortunately for you, mostly 32GB ones) tend to mount/unmount themselves randomly in the latest Samsung devices. It used to be a problem with SanDisk's chips but now, it seems, the phones are also somewhat to blame.
4) Yes, an update by Samsung now allows SOME apps to be installed to SD Card, but if your phone is carrier-branded, it has to wait until said carrier releases it (which can take a while, if at all). In my case, I just got the update last week (Mexico's Telcel).