Make a boot disk with Windows 95 (SYS command) and make sure to copy SYS.COM over to the floppy, too. (just in case ;P)
it's quite simple, actually; all you need is another partition. Install DOS 6.22 onto that partition. I'm not sure if DOS 6 rewrites the MBR on the first partition but if so you can boot to the 95 floppy and use SYS to fix it.
the only caveat being that to boot to the DOS install you would need to change the boot order. I cannot remember how dual-booting worked with 9x, I think it might have been by editing the windows 9x MSDOS.SYS, but I cannot remember.
3. DOS only uses 640KB + 384KB
DOS does. but DOS games for the most part utilize Extended memory via XMS or DPMI system calls. Doom, Duke3d, quake, and countless others.
EDIT: heh, I never actually answered the memory question!
8MB is about "medium" for DOS games. the more advanced games- The aforementioned Duke3d and quake, for example, will run with 8MB, but I doubt it will be very playable. Aside from that however almost any other DOS game will hae more then adequate RAM.