@Liquoricelace ask away!
When I bought my set up, home gyms weren't as common (pre COVID) so suppliers were limited. I bought most of it in one go from strength shop. They're not the cheapest, but they're good, they're based in the UK and I could pick up the phone if I needed to. There are more suppliers now as garage gyms have become more popular , but do look at the reviews. Mirafit are one of the cheapest but can be very hit and miss.
I'm on a couple of Facebook groups, like home gym community, and I'd recommend if you can joining some sites like that so if there are brands you're looking at, you can ask if others have bought from them - user experience is really helpful! Height is a big thing for racks for garage gyms (you can get racks designed for garage gyms which I got, though that's also partly because I'm short and it's nice to have a pull up bar I can reach without jumping!)
Folding racks (that bolt to the wall) are popular now, but honestly I don't really see the benefit - they're to save space, but you need to have the space available to unfold them, so I don't really get how they help!
I'm not personally bothered about attaching things to my rack, as long as I've got safeties (I have webbed straps rather than bars) and the dipping bars. But lots of people do like extra attachments, if you might go down that route, look at the spacing of the holes of the rack, and then Google that + accessories. Then you'll know how universal it is, and whether you can buy add ons from other places or not. Eg 75mm or 60mm is common.
Cheap racks have fewer holes in the uprights - the more holes the better quality the material needs to be to keep the structure strong. It's not impossible to work with fewer holes but it is limiting as that dictates how many options you have for setting the bar at a comfortable height for whatever you're doing.
Also, barbells - there are men's and women's specific. I had only used men's barbells before, but I wouldn't change back now. Womens barbells are slightly thinner, and it makes a big difference for smaller hands! Mine is also a garage version, so slightly shorter than standard, as my garage is old and narrow.
You will likely need more plates than you think, so consider storage (mine are on pins on my rack) Bumper plates are essential for deadlifting, but a bit of a pain for anything else (bulky, hard to move around compared to say, tri grip plates) I started off only with bumpers but then added smaller tri grips as well)
Oh and I don't use a commercial gym at all now. I've tried them occasionally when travelling, and although it's fun to have a bit more variety, having to wait for equipment, or finding equipment isn't good for me (eg I'm 5ft 2, so lots of machines just don't adjust enough for my leg or arm length) is such a pain. The only things I say I miss are having a lat pull down, seated row and a couple of legs machines eg for hamstrings. But I can replicate them reasonably well by using bands looped around the rack, I just don't get the kudos of knowing what the weight stack would be!
Oh and dont do what I did, and buy all your kit before deciding what flooring you wanted! Horse stall mats are a surprisingly good budget option.