First to answer your question,
I don't think a / is allowed in a domain name, however a - is allowed.
People opt for easiest searches, so a domain without a dash is preferred.
In your case since you are using your biz name I think a dash would be ok though.
Now, A few thoughts,
-The point of a domain name is so people will remember it easily, otherwise we are bombarded with hundreds of site names everyday and can barely remmember any of them.
-If your domain name is too long, complicated, or generic then people won't remember it.
-I'd imagine you get most of your customers in this line of work by referals, whether through word of mouth or those who see cars you have done and ask for you.
-the point of having a website then would be to attract those potential clients and show em further. Customers, once established then will search for your site even if they don't remmember your domain.
-I seriously doubt that just a website will bring streams of clients on it's own, unless you are selling products and not services.
-Perhaps used car dealers and car auctions would be a good source for you to find clients.
That's what came to my mind and I hope it is of some help.