I've been in the same boat as you, so I did a quick research I'd be glad to share. Long post ahead.
I started out lower end, and now I have a top of the line Pfaff to work at home.
And the most important thing is the size of the hoop sizes. Most of the intro level machines will probably not go more than 5 x 7, so that will be the largest hoop you can use in the machine. But it's won't be a problem if you learn how to split designs, and then line them up to sew out in multiple hoopings - you will not be limited to design size because of your hoop size (I use Embird).
If you're going to make hats, then you might need a hat hoop as well. Not all machines comes with a standard one, but, personally, I don't think these are vital if you already have worked with embroidery machines.
I'd recommend you to look for a semi-commercial device, Brother PR600, for instance (hard to recommend not knowing your budget). But if you need a smaller machine, then find a Brother or a Pfaff dealer near you. These are the best when it comes to home sewing and embroidery. Brother SE400 or Pfaff 2170 might be a good option if you're looking for entry level.
Here are some sources you might want to check:
https://coldesi.com/2016/12/hat-embroidery-machine-options/ - here is great list of specs you might look for
https://sewingland.org/best-embroidery-machine-for-hats/ - here are some general options and also guidelines for specs
https://makezine.com/2016/11/23/review-brother-se400-sewing-embroidery-machine/ - here's a specific review for Brother SE400 I have worked with
https://sewing.patternreview.com/review/machine/2186 - and here's a review for Pfaff 2170. I hope it's not prohibited to recommend other forums, but sewing.patternreview really helped me in the past.
If you still choosing and need any info, don't hesitate to contact me. Hope it helps!
