You need a lot of money to begin with. For starters, you have to own the building and pay rent to yourself. Very hard to get get buildings zoned for automotive services. Neighbors resist. You need a big floor plan finance program to buy inventory. Better to pay cash, but most use floor plans. Very expensive. That means you have to have a high turn rate. If you have to pay rent, and you need high inventory turnover, you won't make a reasonable wage. You are basically working for your landlord and the finance arms of your brands. Then you don't get to cherry pick the products you want. You buy what they'll allocate you.
I know one fellow who did a great job with it, because I was competing with him. There was a BMW dealership up in the North Shore. The whole thing was for sale at a big discount. New bikes, parts inventory, equipment and customer lists. It had some key employees too. It was a long established store. The problem was that the buyer had to move it. I searched and search for a local building with no luck. The fellow who bought it moved it 40 miles north to a main drag in NH! Presto! Instant success with new sales records out of the box. Not only that but he had a great building and set up a GS test track behind the store. It didn't hurt that he was a master tech either. That young fellow was a genius. That was 2002. The youngster has a couple BMW stores now.
But for every story like that there are 20 total failures. I think you better off buying an existing business than a fresh start up. But either way, you'll make more money teaching and fabbing the stuff you already are.
You mentioned the money wasn't the focus. No job is more hated than the one that doesn't pay you your due. I know that first hand and have seen many others learn the same disappointing lesson. Motorcycle retail stores are hard to make pay.
Straight ahead and faster -Bo Weaver 1970
"There I was..." -Griffin Niner Three Hotel
"One day closer to a parade..." Jonny Gomes, spring training 2013