The SF rear strut tophats are that of a GD stud pattern. So you can either use GC8 suspension and change the rear tophats or go with GD suspension. Most ppl just use the GD suspension (including me). One thing you'll notice with fixed perch WRX sedan style struts is that you'll get some nice *** sag. Wagon springs will help with that. Now I don't know if this is the case with GD fixed perch struts, but with my GD coilovers I had some positive camber in the rear after the install. A $20 set of camber bolts alleviated that problem. One thing to note... both GC8 and GD struts will slam your SF5.
I think WRX AGX struts with Swift wagon springs will give you height and ride quality you want.
The front SF5 strut towers use a GC8 style strut tower bar while the rear uses a GD strut tower bar.
GD sway bars & end links can be used in the rear... even STi sway bars. You'll have to stick with GC8 NA (2.5RS) style front sways due to the NA front crossmember being different than the turbo crossmember. You for sure want to upgrade the rear sway to at least a WRX sway.
The front crossmember on the NA SF5 is just like the NA 2.5RS. If you want to change out your control arms you'll have to use the JDM GC8 aluminum control arms. It’s an urban legend that the aluminum arms are lighter than their steel counterparts. They're just much more rigid.
'06 STi front crossmember w/ steering rack
'04 STi aluminum control arms
'06 STi front sway with Perrin end links
GD Prodrive coilovers (very daily driver friendly and very for sale
GD Cusco rear adjustable sway
Whiteline rear end links
GD Cusco rear strut tower bar