Awesome post! Long time forum lurker here, just expanding my horizons from drop shipping to a few others.
Anyone need any help, hit me up, keen to earn my worth around here
Another tip, pop-up stores are a great way for fast income and quick results...I always found general stores a bit of a headache. A lot of people use general stores to test niches as you say, I like to start with a pop-up or single product store and expand from there. Keep that in mind when building a store, For example the pet niche is supersaturated obviously, but if you were to start a single product store and got results, your pixel data, social channels, and email list would all grow with pet lovers and you can add more products from there without having to start a new store.
There are a few affiliate apps offered on Shopify now too, they cost a pretty penny BUT if you want fast turn around, set up ad campaigns or get influencers to share posts promoting your affiliate network, once that gets out there the ongoing traffic as a result is essentially priceless as it dosent end until those affiliate posts stop getting shared.
Those are just my 2cents though, hopefully that helps.