I run to small sideline business, the first is beachcombing and making art from my findings, and it is a lot of work.
I comb for all my stuff, photograph it (for calanders , selling prints) , make art from it to sell, teach small classes on beachcombing and beach crafting, and sell the driftwood and seaglass as well. I also wrote a short guide book, and answer questions on my page.
I also thrift and flip small collectable items like vintage dishware, bags and clothes that have a high mark up.
So far I have learned that you need to be using the right platform to sell, I wont sell heavy items on Ebay, because of their shipping costs/relists, and I don't use Etsy anymore because I was losing too much of my profit margins in my cut to them.
I mostly use my FB page, FB marketplace, and local selling pages, as well as Instagram. It keeps the costs down, and matters.
When you sell something, ask the buyer to leave a review, and follow up right away of there is an issue.
Holding sales on a different featured item each week/month allows you to remind people you are there, contests (occasionally) where you share, like and follow to be entered are useful.
I do craft shows, but only a few now, as they can be costly with table fees, travel costs, display sets, food while traveling, extra staff etc.
I stick to ones that do well every year, and have mid range table fees.
Keep a close tab on your spending, keep receipts, and be honest about how bad things can be, before you would stop. Are you using family money to support a business, what it the timeline to pay off any investment costs, etc
Talk to people doing what you do, locally. Network, go to peoples shops, or markets, see what it compares to what you have planned.
Sorry for going on, it's been a passion project for me!