You've figured out the most important part: planning. You're asking questions, you're challenging yourself, this is how successful people operate. I've read a lot of case studies for similar sirt companies and people just one day decide "I want to sell shirts" and they just go ahead and do it.

I work in marketing and this happens all the time, across all sorts of industries and business types. It's especially prevalent in small businesses. If you're selling an actual product - for example, a bacon clock, a thing I just made up in my cunty head - and you sit down with the creator and ask them who they want to sell to, they would say "anyone, everyone, anyone who wants a bacon clock, bacon lovers." It's too vague, and in doing proper research you may some up with new ideas.

You would want to sit down and ask "are these younger people or older people? What sort of economic class? Would students love this, young professionals, newlyweds?" The whole idea is, you do not need to cling to this group, it's just a starting point. Maybe in this research you stumble across a totally untapped market.

When I meet with clients, I would tell them that it doesn't matter how small your market is as long as you own that market, meaning you're the best and most effective seller for that group. If that means you're trying to sell the best and most popular shirts for suburban hip hop fans, or the best hats for urban Asian gamers, you can grow from there but it's good to start confident. Other companies, they just open a store and hope people come.

Anyway, good luck with the thing, I'm just dumping walls of text like the fucking quivering ghoul I am.