i suggest you do some research.. 12k would get you a r33.. if you just wanna go fast.. then you'll end up losing something quite quick..
start with a stock car and go from there.. you won't (shouldn't) lose control of a stock r33 gtst.. check out the events in the queensland section for places to go, meet ups etc.. for insurance, find the car you're interested in and call and enquire about third party..
in terms of maintenance i'd say it all depends on how you drive it.. so far i've only had service costs (2yrs in r34, but i drive prob once or twice/month