SDHC stands for Secure Digital High Content and it just allows you to break the 2GB barrier. No cards at 4gb or more are just SD. They are the same physical size- and SDHC card readers will see a normal SD card. But you can't see the whole 4GB or whatever size on regular SD readers. This may concern you, but using the included USB cable will make any card in your device show up in your main PC as "removable disk" under My Computer. Then you can drag items from your PC and drop them onto the removable disk (probably drive "E" and "F".) This negates the need for a card reader at all! Plus, you don't need to remove the cards from the device, so you will have longer-lasting cards and the slots won't wear out.

Worry not about damaging the card by putting it in the device. Just install it and go.

They don't corrupt easily or at least they are just as likely as the smaller capacity SD versions. You already know what the difference is now :0)

I don't know about an "official" one, but any one you can find that is bigger than the size of your screen will work if you trim it. It comes with one already, unless you pull it off. I used the protector on my old PDAs very rarely and I didn't mind the tiny scratches since the protector scratches fast anyway. Might as well just deal with it....
Once mine is too scratched I'll probably just leave it off. The HP RX3715 I had for two years, never used a protector at all and the screen was nice enough to sell on EBAY as nearly new.

The backup feature is there under settings>backup/restore. It will save your settings and documents/pix on the device but won't be a full backup. Remember that you need to use the removable card as the target for the backup if you decide to re-flash the unit with OS200x.