For the front of the car, you will need to change: Struts, lower control arms, spindles, brakes (calipers, rotors), hubs, and tie rod ends.
For the rear, you will need: Backing plates, hubs, and rotors.
Now I will break down which donor cars you can get the parts from.
Lower control arms - XT6 2wd/4wd (the ball joint that fits in the right spindle is too big to fit in the stock arm) If using 2wd XT6 arms, please be advised there *may* be an issue mounting it to the crossmember. Hondasucks encountered trouble, I however did not.
Spindle - XT6 2wd/4wd and GC8 Impreza
Struts - XT6 2wd and GC8 Impreza (note that if putting imprezza struts onto the XT6 spindle, it is advised to grind the spindle down slightly for ease of fitment)
Tie Rod ends - XT6 2wd/4wd
Rotors - XT6 2wd/4wd and GC8 Impreza (please match rotors to which spindle you use)
Calipers - XT6 2wd/4wd (even if you use the GC8 rotors, the calipers are identical, aside from the XT6's still have the ebrake in the front)
Hub - XT6 and GC8 Impreza (please match hub to which spindle you use)
Hub - XT6 4wd
Backing plate - XT6 2wd or 4wd (2wd requires modification)
Rotor - XT6 4wd
Calipers - XT6 or EA82 (they are identical, you can reuse your old ones if you have rear discs)
So now for some tips on the conversion.
1. Where it says on the front control arms and how Hondasucks had problems with a different size bolt, I had the same issue and since I was the one who modified the crossmember for Hondasucks's '87 GL turbowagon, I did the same thing for my '89 RX. I drilled a larger hole where the bolt goes through the crossmember and through the control arm to 1/2". Then, I welded washers with the original bolt from the original control arms (regular EA82) onto the crossmember at the bottom of the hole I drilled (put bolt through the washers and through the crossmember with the washers on the outside of the crossmember). Made it work pretty easy and the control arm doesn't rub on the crossmember. He's been running like this for a couple years now with no problems and that includes a couple rallycrosses.
2. Next, if you plan on using Impreza struts in the front, you either have to A) modify the strut tower on the vehicle to match it (ream out a couple holes for the studs on the tophat) or change out the Impreza tophats for the EA82 tophats. I did B on my RX and I had no issues running the EA82 tophats on the Impreza struts. ***NOTE*** If you plan on modifying your strut towers for the Impreza tophats, you then have a wide access to upgrading to camber plates made for '93-'01 Imprezas or Legacys.
3. If you plan on running an Impreza coilover setup, it'll bolt into the front with the strut tower mod listed in #2 but the rear is totally different EA82 vs. Impreza. The rear will fit nonetheless BUT you HAVE to use the original EA82 tophats in the rear. I have yet to do this portion of the conversion and I have only read that it would work so I have not yet found out myself if it does or not.
If you have ANY questions, PLEASE feel free to PM anyone on the board that has done the 5-lug conversion and they'll either be able to help you or send you in a direction of another board member to help.