To be honest I would say it's something you work towards gradually and space out dye and bleach sessions 4 weekly.
It also depends what has been done to your hair in the past? has it been dyed? And how long ago did you have blonde before. All the previous work done to your hair can affect what colour it goes to.
Really I would visit a hairdresser and get the intial lightening process out the way, and let them know you want a colour that would be easy to upkeep at home yourself with box dyes/lightening.
You shouldn't use anything more than 20vol (6%) peroxide on your scalp at home. You run the risk of damage to the hair and chemical burns. Anything higher is more for off the scalp techniques. I've had chemical burns with just 30 vol in a salon, and I had to sign a waiver because i made them use it
Never again!