well whatever u like the look of, pick a couple of shades lighter as it wil always go a little bit darker than on the box. when i did mine i wanted "rhianna red" hair so used 2 of the color b4's, then a lightner kit, and that took me from a dark plum/purple to a light gingery blonde colour.
i used colours straight after tho, although it does say to wait a few days to help replenish ur hair but your hair doesnt gain much from a couple of days. as long as u condition it will u will be fine.
i thought you could use bleach as long as u keep well ventilated? obv im no expert tho!!
the nutrisse colours are good because they are really conditioning, id stay well away from the xxl as they are full of silicone which coats ur hair if you use straighteners, and makes it almost impossible to remove at times, so colour just builds up and gets darker and darker.
if your wanting to stay a light brown colour then try a dark blonde with ash in it, that would go a light brown colour.... or if your wanting a bit of reddish colour maybe try nutrisse 5.3 - i used that and its a light brown with a reddish warmth in it xxx