I think you have already had some good advice but would add the following:
- As well as rent you have business rates, employee costs, marketing, maintenance of the site, insurance, licencing, theft, vandalism........
- I ran a very successful business in London back in the 90's, we had a niche Franchise, tiny showroom you could fit 4 cars in. We had 6 parking spaces close to the showroom and the rest of the stock I kept miles away in a cheap space. Customers would call from the adverts before they came to see the car, so we could move it to the showroom or take the car, as we usually did to them. I knew, sounds arrogant I know, exactly what the market was and only stocked petrol and Auto SUV's and MPV's, I would buy others, but move them on in the trade for a profit, with the premise being the trade account will always cover my salary and associated costs.
- Managing, recruiting employees will eat your time like you won't believe and getting others to share your values is key.
Keep us posted.