I would strongly recommend NOT buying a 335i as your first car. The insurance price is mental because the Insurance company is reasonably confident you will stack it. A first car will generally see a ditch or two, be scraped against a couple of walls, bounced up a few kerbs etc - you can't do this sort of stuff in a 335i.
Not to mention the fact that you'll have more than 300bhp, going to the rear wheels, under your foot and absolutely no experience of how to control this.
FWIW I think you're doing something wrong to get an insurance price of £3000. I paid £1200 for my E46 330i at 21 with 0NCB. Last year on my 335i I paid £715 with 2 NCB, 24 yr old and cosmetic mods declared.