[Tutorial] Installing rxTools Custom Firmware - (3DS and 2DS) this link has the answers for questions 1/2/3/5
as for question 4 its just a matter of installing themehax (requires systemnand 9.0/9.2) and grabbing another rxtools loader file stored in a .3dsx (homebrew)
edit:
if you want short answers
1 A nand is your system's firmware. A emunand is an emulated copy of your own nand. nands are linked by default and there is a simple process to unlink them. and unlinked is better as there are often errors associated with linked nands EX: some games appearing "wrapped"every time you power on system
if nands are linked they share a folder (with a unique id) on your 3ds for extra mem / saves and other files when you unlink you create a new one for your systemnand. leaving your old one to be for emunand alone
2. that card should be fine and whats more if you have a ds flascard that was blocked by a 3ds update you can install a file called bluecardfix.cia to re-allow it
3. yes sir
4. "as for question 4 its just a matter of installing themehax (requires systemnand 9.0/9.2) and grabbing another rxtools loader file stored in a .3dsx"
5. the link i provided has instruction and
a lot of info as well as a helpful maintainer
2nd edit: sorry for my bad spelling, grammar, and punctuation