good luck!
its a very difficult game to get into now.you will not be able to price things the same as the more established car dealers locally so will probably struggle to buy cars,advertise and prepare them for sale and still make enough to pay you a wage after paying your overheads.especially when they bring them back with issues that require putting right which can eat up any profit.
i set up in car sales in 2004 dealing primarily in ford rs cars-this went well for a couple of years as the rs market was still popular but it began to tail off(cars were harder to source for sensible money,buyers were turning to saxo vtr's etc instead of rs turbos and imprezas/evo's were replacing cossies as the choice cars).i tried to follow the trends with the sports stuff but it just plodded on rather than make money.
from mid 2008 when the car game went tits up and the only stuff selling were cheaper runabouts or more sensible diesels rather than the sporty stuff, cars were almost impossible to source.
i gave up towards the end of sept 2010 when i had run out of money.

i now work for a large (well,40+ cars on site from £995-£45000) car sales garage in their garage.they seem to be doing ok but they have been established 30+years.they give 3 months unlimited warranty,12 months mot with every car and they do charge top money for their cars-but they do sell them(prob 30-40 per month).i would never have got the sort of money they get for their cars.

i wish you all the best in your venture but if asked wether i would start up again i would have to say i wouldnt.it becomes a 7 day/24 hour job and if you have a concience or are subject to getting stressed out then youre doomed!im happier and more settled now than i have been in the last 5 years.i shut off at 5pm and have family/chill out time,and my wage is steady(ok it doesnt have the highs of selling 5 cars in a week,but it doesnt have the lows of not selling a car in 2 weeks and looking to sell them for less than you paid just to free up some cash).

hope some of this makes sense!......