1) That is a subject of personal preference. Try both and decide which one you like.
2a) No, it is not applied to the daily builds.
2b) Is the memory necessary? No. Rockbox runs just fine with only the 32 MB of the standard iPod Video build.
2c) The memory does not allow things to run faster. It provides more audio buffer. This is not
always a good thing, as filling a large buffer can waste battery filling the buffer with longer drive access if you are only listening to a few songs, or if you change playlists frequently.
3) Nothing saddens me more than people fresh to Rockbox rushing out the unsupported builds - for three reasons.
Reason 1 is that they often never learn the ins and outs of Rockbox, and get confused over what is Rockbox and what is (insert unsupported build name here.)
Reason 2 is that they tend to expect support from the unsupported builds. Be that support from the core Rockbox community, or be that support from the kind souls who offered the unsupported build as an act of kindness.
Reason 3 (the most important one) is that Rockbox (except on the Archos) is not a release-status project. It is an actively developed project, in constant flux. I'm having trouble expressing my thoughts, but Rockbox could really use more people ahh forget it4) There are sooo many Gameboy games, I have no idea what ROMs you have successfully copied from your carts. Many don't run 100%, but are still playable. Trying is the best test.
5) Don't know.
6) Correct.
7) Read the manual. Read the wiki. Search the forums. Then ask questions and you will be loved the world-round!

PS:
Oh! If you read the documentation and still have a question be a good lad and report where the documentation was lacking so things can be better for the next person to stumble by! Thanks!