Single guitarist double tracking/re-amping advice...

If you will reamp them thru a tubescreamer or a higain amp, both have an input drive knob, so it's not 100% necessary to normalize the DI-tracks. And I would keep the settings relatively similar, but try which sounds the best. You can always reamp the guitar tracks with like 6 different settings and then choose the best combo in the mixing situation.
 
The best thing about DI's is that you can go back and change things if you don't like what you come up with. I like to quad track with different amps so the overall tone is symmetrical, but I notice some mixers have different tones left and right. It depends on the vibe and what you're after. And don't normalize. This will change the character of the parts. If you have trouble driving the amp properly, either you've recorded them wrong or there is a gain staging issue in your signal chain.