I'd 2nd just about everything that Superhuman & Benoit mentioned here.
I'm also a big fan of doubling up all the rhythm tracks and panning them pretty hard right & left. I rarely go the full 100%, since in my own experience it can cause the guitars to lose a bit of their overall punch. But then again I am working with just about the cheapest setup you can get. LOL :o

For rhythm tones & effects, I would almost always go as minimal as possible...doubly so if you are really planning on doing some serious layering. Nothing produces sonic mush quicker than 4 guitar tracks with reverb, chorus & delay piled on each of them. I used to be a huge fan of chorus effects, but these days I try not to use any at all on the rhythm tracks....Usually just some BBE Sonic Maximizer to brighten it and make it project a bit more.
Also as was previsouly mentioned, try a little brighter tone than you might typically expect use much less distortion that normal...again, especially if you plan on piling on the tracks.

For effect units/preamps/etc....I know that I'm still a bit behind the times perhaps...but I still swear by my Johnson J-Station and my POD 2.0. I love the V-amp2 as well...but those things just do not seem to be very durable. Too much bad feedback about them crapping out for no reason at all (mine did too).
With either the POD or the J-Station, I typically like to do 4 rhythm tracks;
2 with a Rectifier type setting for the grind and 2 with a more upper-mids based Marshall type setting for more punch and clarity.
Here's a Testament cover that I did using the J-Station for all of the rhythm work....LOL....Actually on this particular tune, I also did 2 bass tracks one dark sounding one for the "thump" and a really bright one to get a little of the classic Greg Christian sounding "clank" on the bass. LOL

Sins of Omission Cover

Bear in mind that it's a soundclick player..which kinda schmuffs the overall sound a bit. :mad:

Don