Keep it small, build up stock and grow as and when you need too.

Do a mix of vehicles, keep the market open, but could specialise in a few makes.

Ebay would be a good way to keep stock moving and reach nation wide audience, plus get a website done )maybe one that you can constantly update yourself and have the link on the ebay auction.

The servicing side will mean alot more in terms of land, insurances equipment etc etc. but could be something to expand into