1) You don't need a quad-core processor to multibox, however, the least I would use is a dual-core processor with 2GB RAM even for minimal dual-boxing, but a dual-core can also quad-box just fine, in my personal experience. You can use multiple computers and link them together through software or hardware. I have tried dual-boxing with 2 GB of Ram on a Single Processor, but I did not have much luck, and experienced several problems.

Using Processor Affinity, you can apply certain WoW directories to certain processors.

2) The problem with auto-follow, in my personal experience, has had to due with what kind of set up I was using in terms of a computer. I had a problem of losing my fourth character all the time when I quad-boxed with 2GB of RAM. When I upgraded to 4 GB and bought a new video card, I no longer had that problem. And again, I've five-boxed with five simple 1gb single core Dell "Back to School" computers, and didn't have the problem.