I was relaxed for YEARS and now I'm a natural who keeps my hair straight 100% of the time. To answer your questions...
1. How often is too often for washing? I would like to wash/deep condition twice a week.
I washed my hair every 7-10 days depending on how much sweating I did. Anything more often then that I would experience dryness because my hair is a very thick and dense 4b that I have to really work to maintain moisture levels. You really have to do what works for you because there are plenty of relaxed heads that can sustain that amount of manipulation.
2. How do you preserve roller sets?
I can't really answer this because I never wore roller sets. I wrapped my hair each night and combed down in the morning.
3. Do you have one tip that you wish you would have known a long time in managing relaxed hair?
To be honest, I love wearing my hair straight and have learned that I am able to manage a sleek, bouncy, flat iron with my natural hair just like my relaxed hair. I wish I had known earlier that I didn't really need to chemically straighten my hair. I also wish I would have avoided all of the bandwagons when I first became interested in caring for my hair. I thrive best off of keeping it simple.