I worked in and managed a hobby shop for 12 years. My username comes from that era. Kids would see me around town and whisper to mom or dad, "That's the Toyman." That job was my favorite job. I honestly loved everything about it. My plan was to buy out the owner when he retired but the industry changed and I couldn't make the numbers work. I would have been trading nickels for nickels. The only reason Randy's was able to stay in business for as long as he did is he owned the building he was in, it was a corner lot in a very touristy area, and he was a bit of an icon in the area after 30 years.
He ended up with cancer and closed the store not long after that. This was shot just before the building was torn down.
At that time, magazine companies were selling for 2%-3% more than we could buy products for and everyone wanted you to match their pricing. You can't keep the doors open for 3%.
The distributors you buy products from are the online companies you have to compete against. Great Planes is Tower Hobbies. Horizon Hobbies didn't even bother to change their name. Hobby Town will sell you a franchise and then turn around and compete with you online. That makes for very thin margins.
It's a pretty cutthroat business. You will be hard-pressed to make it on just RC hobbies or trains. You are going to have to sell everything. We sold kites, beach toys, plastic models, lottery tickets, paint, trains, planes, boats, cars, wooden models, rockets, yo-yos, pretty much you name it. Randy had a saying, "If 3 people come in and ask if we carry dog E36 M3, the 4th person will find it on the shelf." Which leads to the next problem. You are going to have to stock everything. At any time we had $175k-$300k in merchandise in stock. The instant you tell someone you can order it, they are gone because they can order it too, and probably for less than you are able to sell.
Lastly, it's retail and all that goes with it. Plan on working every weekend, most holidays, and Black Friday. Don't forget Christmas Eve and the day after Christmas. That was the one part of the job I hated. Unfortunately, all of those days are the ones that pay the most.
So, can it be done? Absolutely. Can you get rich at it? I didn't think so. Would I go into debt to open a hobby shop? No way. Not in these days of cheap online sales. I wasn't sure I was going to be able to feed my family when I was running the numbers much less service the debt.
All that said, do some research. The industry has probably changed a good bit in the last 20 years. It may be more feasible now than it was when I was going to do it.