I've never found a good guide on how to get started in hardware or eCommerce, but I've been posting yearly[2], monthly[3], and weekly[4] updates about my experience learning as I go.
One thing I wish I knew at the beginning: it's difficult! Scaling a hardware product is probably 10-100x harder than scaling a software product. There's nothing like GCP or AWS that scales from one to thousands. Vendors that offer fulfillment services won't work with you when you're only selling tens to hundreds per month, so you have to do everything yourself. I built my own fulfillment center[5] and hired people to staff it, and that's complicated because that gets into inventory management, employee payroll and benefits, insurance, etc.
The difficulty is a double-edged sword, though. It prevents people from competing with you because nobody else wants the hassle. But the downside is that you're the one who has to deal with the difficulty.
[0] https://news.ycombinator.com/item?id=23927380
[2] https://mtlynch.io/solo-developer-year-4/
[3] https://mtlynch.io/retrospectives/