Yep a hobby can absolutely become a business, some good advice is:
- Keep doing your day job and build it in your spare time
- Try switching your day job to a 4 day week once you can afford it, if they will let you. That extra day is very useful.
- Always keep in mind and minimize how much manual processing work you need to perform to turn goods you source/get made into products that you can ship.
- Don't put off getting china to make small bits and prices like wiring looms to save you time crimping them yourself. It usually ends up costing the same if you by lots of 200+ as china can get the parts cheaper and that compensates for the labor cost.
- Don't try to optimize your BOM cost to the nth degree from day 1, keep parts simple and easy to get and start selling your product. Once you are selling a good amount then optimize it.
- Sell for no less than 2.5x the cost it takes you to make it. If no one will buy it at this price then you need a different product.
- For any components that have long lead times, when you buy them and they arrive always put a percentage of them in a different box with a note "ORDER MORE NOW" (alternatively you can use an inventory system but you will forget to order long lead time items unless you have a system to remind you)
- Avoid using ongoing subscription services, like... Shopify is easy but it has a monthly cost, or you could make a simple HTML/PHP website and use paypal buy buttons or their cart system for free.
- Try avoid making products where the intended customers are the general public. Best to have customers who have a more specialized interest, with a brain.
- Check with your local city/govt about how to start a business and what are the traps. Sometimes you pay tax in advance, so the first year that this kicks in your paying tax twice, for the next year and the current year. That may not apply to your country, but it's the sort of trap you want to know about before hand.
- Get a proper shipping account or atleast enquire and find the pricing. Its often way cheaper to send direct through DHL/Fedex/UPS instead of taking goods to your local post shop. And DHL/Fedex will pickup packages.
- Don't lie on value on your export customs invoices for customers, You are taking all the risk and they are getting all the gain.
- Dont mess with mains voltages yourself for your product!!!, source a power brick with all the needed certification already done to ship with your product.