Mainly just greater availability in knuckles with Macpherson strut as R32 knuckles are notoriously shit to weld
Double wishbone does tend to have more lock out of the box / with minor mods and they don't tend to need as much camber to get a decent contact patch: -5 deg on Mac strut is = to ~-3 on Double wishbone
If you find some good R32 knuckles (either cast from scratch or welded properly) then stick with double wishbone, otherwise go Macpherson.
As for how to do it, i remember coming across a guide so will try hunt it out, but the hardest part is drill the top mount holes (hubs bolt up to LCA and tie rod ends are the same). If you want to run a swaybar then you need to get Silvia/Laurel lower control arms. IIRC the front R32 hubs won't fit the Silvia hubs so S15 or C35 hubs are needed