Hi, and welcome aboard!
Redhat 8 is, AFAIR, 32bit, so you wouldn't need the AMD64 nforce drivers, nor could you use 5332. You should use the x86 nforce drivers, and 5336 for your Geforce.
1.) No, not really. Even sound may work with ALSA, but I don't know about ethernet (I use a Tyan board with AMD chipset). The instructions supplied by Nvidia are not that hard to understand, what exactly du you want to know?
2.) No, cause AGPGART is part of your kernel. But I think there may be problems with the 2.4.18 AGPGART and your chipset. I would suggest updating Linux to some 64bit distro based on kernel 2.6.x first.
And well, the only distro for AMD64 I could suggest right now would be gentoo (everything 64bit and kernel 2.6.1 with AMD64 fixes) - have no fear, it's not as hard as most people think. The installation instructions are top-notch, and the gentoo community is really great if you have any problem.
Maybe I'll see you on forums.gentoo.org, 'Gentoo on Alternative Architectures' anytime soon?