Alright, so I think I'm going to buy some coilovers next week and I have a couple questions.
As far as a DIY install, how hard is it to complete and how long would you say it takes? Is there anything else part-wise, aside from what I would get with the coilovers that I should go ahead and purchase? Also, I have never really looked into them and need help with deciding on a make. I drive an ST204 so my options, it seems, are Megan, D2, XYZ, Ksport, or BC. Opinions?
As always, thanks for the help.

I hear the BC give more rear camber than the Megans.

I would definitely pick up a set of rear end links (Racing Beat Miata ones).

If you haven't touched your rear suspension lately, you'll want to pick up a new set of sway bar end links. They have a nasty habit of seizing up then breaking free inside the joint so they spin freely and can't be removed without cutting them off.

Time wise, you may spend anywhere between 10-30 minutes per corner, depending on how quickly you work. If the rear end links cause you problems, you may spend more time back there while you cut them off.

Excellent. Thank you both!

I've got BC V1's. They are very good, nice and stiff when you need them to be and comfy when you need them to be.
Rear wheel has neg3 degree camber though. Needs camber bolts to fix it but cbb lol
These pics show what I mean: