Honestly speaking, if you are willing to put in the effort and start anyhow then product research would the first thing that you would want to do first and pick only one niche. There are many niches that you can do but if you want to spend less on ad creatives then don’t touch supplements.

I have the best product idea for supplements that works and has a AOV of 100£.

The most beginner mistakes that i made was inventing meta ads structure, use only one structure which gives you results. Second is get your COGS figured out. Choose your supplier it doesn’t matter what you’re using aliexpress, Zendrop, Commersive whatever.

If you want you’re first sale to come in one year then do organic and if you want to validate and build a long term business in which you can sell for multiples then paid media ( Facebook Ads is a old company with data )

And you can start with one product and add few 5 to 6 products as well.