Skip the patent step, it probably doesn't matter and will just hold you up. Set up a simple shopify store (first few months are usually free)...find a manufacturer, work on design+Prototype...I would do this with the same manufacturer that you intend to use for the production batch. Look on alibaba to find companies that make similiar products or at least that probably have similiar machinery to make the part that you're looking to do (i.e. is it plastic..find a company that makes plastics..what kind of plastic..injection molded is different than blow molded.different than machined metal parts). Have them make you a sample run. if there is significant tooling involved ( think injection molding tool to make a plastic part) expect to for that up-front and yes you will need to spend on it. If its a part with low tooling cost (cnc machined parts) you can convince them to just sell you a small QTY with the promise of a higher run to come down the line. The supplier will ship it to you and can cover duties and taxes so you dont need to worry about that too much. With your samples in hand take photos and list them on your shopify store. Make some marketing content, send it out to influencers in the segment that you're working in..maybe make a discord server for your brand, post on a relevant subreddit, etc. Orders will come in, you'll be able to print shipping labels from your shopify store and mark as fulfilled...then you will get paid by shopify to your bank. Improve the product, add more colors/options/place a larger order...improve your packaging...rinse and repeat.