I'm a mediocre sew-er, but I've learned a few things.
I agree that you should definitely look for some sewing classes. I'd love to take some, but there aren't any offered in my area. I learned to sew from my mum, she used to make all our halloween costumes, matching dresses for me and my sisters, and a bunch of house things (curtains, pillow cases, etc.). I find the info I know usually comes back to me right after I've finished sewing a seam wrong, lol.
I'd suggest going to a sewing/fabric store before you buy your machine. Ask if you can 'test drive' a few, and see how simple they are to thread and use. If you've got a place nearby that does sewing machine repairs go visit them too - they might have older models for sale at a discount AND will be very comfortable with telling you how they run. Even if they don't have anything, knowing the people who can give you a tune up is very useful. (I cheat and use my dad...but my sewing machine is 30 years old.)
As far as supplies, extra bobbins are a necessary thing - especially if you want to use different colored threads with different fabric colors. As far as I know they're all standard - at least I've never oopsed and bought ones that didn't work!
I'd also get a wax pencil. TBH I use a sharpie on my fleece, but I'm also careful and experienced enough that I remember to leave seam allowances (even if the pattern doesn't mention them), and to only 'color' on the wrong side of my fabric. If I'm making anything for myself I ALWAYS use a wax pencil or chalk to mark the lines rather than pen or sharpie. I can handle putting together a cage liner, but I'm much less confident on anything more complicated than a pillow case.
If you can't find any sewing classes near you think about buying a basic sewing book - even look for old ones at thrift stores! The info is largely the same (as far as how to fit something, put a pattern together, etc, less so for how the machines work.). I have this one: (broken link removed) (but my version is about 40 years old
Thanks Grandma! lol )