Yes the AMD 64 3000+ has the 1 MB of L2 cache. As for the ram, a single chip is mariginally faster than two chips if they are not in dual channel, but I doubt you will notice the difference.
Personally I think the dual channel makes a big difference. On my old computer I was using 2x256MB DDR2100, my motherboard crapped out on me, and so I purchased a new motherboard that supported dual channel, with the same ram with dual channel enabled, my PCMark 2002 score increased 500 points.
Also, I posted this in a another topic too, I have a computer with a 2800+ XP chip, and one with a 3000+ 64-bit chip, the 2800+ chip scores almost 900 points higher on PCMark 2002 than the 64-bit chip.
As far as the motherboard, I can't speak from expierence. My question is why? I have messed around with overclocking some just to learn, but I have never had a reason to overclock? I ran a 2100 chip for quite a while on all sorts of games, have recently upgraded to a 2800 chip, and have never run into any performance issues?