From my last experience I highly suggest to stay a ways from dying. I got shafted in an order from BA and it was lighter then my normal hair. So I darkened it with perfect 10 hair dye. A week later its back to light. So I used it again and this time used the conditioner it comes with. That lasted 2 weeks. I have been doing this now for a month and a half ( waiting for my TL order ) and it just not working out. That said...
1) you can only go light to dark, if you go the other way you need to involve bleach. I actually used a 10 to 1 mixture of bleach to light my hair and I was happy with the results.
2) This depends on the dye. Perfect ten tell you to leave it in for ( I think it was 2 minuets ).
3) Perfect 10 is what most people suggested for me. I wish I knew what the factor used, because it lasts.