Re: Rhythm Guitar
A drum machine, preferably with a "human feel" option than factors in the realistic minute changes in tempo real drummers have and that keeps it from being overly mechanical.
Years ago, when I came to the sad relization I just didn't have what it takes to be the Shredder I wanted to be, I decided to focus on being the best rhythm guitarist ever. I learned all the rhythm parts to all the songs I could find (stacks of Iron Maiden, Black Sabbath, Judas Priest, Alice Cooper, Twisted Sister, ACDC, etc).
When I got into a band, the drummer was highly impressed that I could keep the song's tempo when he dropped a stick or had some other malfunction that interrupted his playing, and that I could jump from "2 and 4" to "1 and 2" in the blink of an eye, which changed the feel of the song entirely, yet he continued to play the same thing.
Ignore the fills and runs and solos, just focus on the rhythm. Hit when the kick drum hits. Once you've got that nailed, hit when the snare hits instead. Once you've got that down, alternate between keeping up with the kick and the snare in the same pattern.
Switching to Bass for a while will also help your rhythm chops a lot better.