1. Pretty much anything goes. It's V9 and the newer models that need a bit more specific patching.
2. The "old" mode was left in just for the case if there is any need for it (so far there hasn't been).
3. The MDMA/UDMA are the hard disk drive data transfer modes. New modes are developed when newer, faster drives are designed. By changing the transfer mode the HDD can be forced to behave like an old slow drive (when certain games rely on the speed of the original CD/DVD).
4. To use the REAL original HDLoader disc for patching requires a bit more dedication and understanding. If you don't know how to program for the PS2 you pretty much can't do that either then.
--- Signatures are just lame excuse to waste bandwidth ---