RH6 is quite old and installation of many newer programs can be hard (newer libraries required).
a) No problem, install pppd and any dialler (or even without a dialler)
b) X Window, small window manager (Window Maker, Blackbox etc) and a browser (rather something new, downloaded).
c) Choose "Development" during install.
d) Chose "Web server"
e) I think there's "SQL Server" section to choose, if not, you should search for an SQL (MySQL, for example).
f) Installed by default (network client)
2) Yes, it's always a good idea. AFAIK 6.0 uses one of 2.2.x series, so you'd rather stay with them (upgrade to 2.4.x is possible, but not easy for a begginer, leave it for now).
3) Many programs will ask you about newer libraries. that's why it's a good idea to use RH 7.3 or 7.2
4) Bash is installed by default.