Websites are cheap these days... $35/yr gets you started, $100/yr is more robust... but if you're selling product and will be producing it, make sure that part is working okay before getting into the WEB. One thing about internet biz is FAIL is/will be written/blogged/emailed by dissatisfied customers more than a "Good job!" report.
On-line biz is no different than real world biz... have a plan and go from there. Wishing all good luck! (I speak from experience as regards COMMON COMMODITY... had a B&M antiquarian bookstore for a few years and did the web for two and ALMOST made it, but B&N and Amazon did it better and it was quit or go broke.)
You'll make a little money... maybe a lot of money... for a short period of time. It is the LONG HAUL that counts. Take that into consideration for the biz plan. Cautionary statements, of course, but the real thing is JUST DO IT! Do it as far as your bucks/time/personnel allow.
Marketing and product are only part of the equation. Lining up a method of payment is the more difficult part, and brings in new level of security requirements, etc. Shipping. Returns (should be none if clothing, make that part of your sales NO RETURNS). Fraud. Copyright and Trademark. Taxes. Then multiply all the above if going international. :)
All above is doable. But it's not like setting up a lemonade stand outside the parent's house where things are neat and simple... ecommerce is Business and all those things that apply to a B&M apply to an internet biz.
Might even need an attorney and an accountant.
Just things to think about. And you did ask. :)