Mr Wilks is spot on with that view if you want to commit to getting into detailing. I’d not rush into buying everything up front as, for some, detailing takes a lot of time and some can’t be bothered. Get your wash technique right (1 bucket for wheels, 2 for bodywork) and once you have this part sussed then I think you’ll need a DA machine as the more you detail it, the higher level of perfection you’ll want and a hand polish on BMW paint is pointless at removing swirls.