As someone who's actually starting something up. You're making a fantasy in your head and not a real product.
Do you know any of the fundamentals of tailoring/seamstressing? Do you know the fundamentals of how a business works (cash flow, materials cost, time investment, taxation)?
To use myself as an example, I have design documents on my desktop and loose measurements on paper. I've ordered the materials to make my product prototype and I know how to use the tools I'll need (sewing machine). I've got people already waiting to see what it will be like (marketing) and some who are keen to order (investment). So when I have the prototype done, my investors can pre-order. I can then bulk order the materials I need, keeping costs low for my customers and a healthy profit line for myself. Most importantly, I've got a spreadsheet ready so that I can declare to HMRC how much my little business venture is paying. There's no point getting a business going, then having it killed by back tax.
I've planned everything, I know where I'm going and what I'm doing. You need to be the same if you want a chance of actually creating something successful. Youtube and your local community college is your best bet for a lot of these things.