Hi Cody,
Lots of good advice in the previous responses. I agree that opening a hobby shop requires a lot of upfront money. Here's a few ideas that aren't so capital intensive in no particular order.
Start an online only store. E-bay, Facebook Marketplace, etc.
Sell at train shows / swap meets. Here in So. California, we typically have at least two Great Train Shows each year. I've met several sellers who travel around the West Coast selling trains and accessories at various shows. They acquire inventory from people they meet at the shows who are looking to sell collections quickly.
Watching the OGR wanted-to-buy / wanted-to-sell forums will give you a pretty good idea of what people want and what they are willing to pay. I met a seller at a train show who inherited his brother's extensive train collection. Unfortunately, he had an over inflated idea of the value of those trains. I rarely saw anyone buying anything from him. Yet he still showed up at all the shows.
Look for a good book (lots of 5-star reviews) on how to start a business.
As someone mentioned previously, get some experience working at a retail store (doesn't have to be a hobby shop) and ask about managing inventory, cash flow, staffing, etc. You'll get a real education.
If what you're really after is meeting some like-minded train people, then look for a club where you could get together occasionally to run trains and socialize.
Good Luck!
John
