to answer all this question. refer to the officical japan website. Even though can't read japanese but it shouldn't be too hard to guess.
http://www.subaru-sti.co.jp/parts/catalogue/index.html
http://www.subaru-sti.co.jp/parts/gdab_impreza/cat7.html
Yes the S202 share the same Spec C RA engine, same turbo (VF34) but better ECU tune and sti goodies.
Yes there is V7 STI wagon code GGBA5EH and GGBB5EH depend on the production year.
There is a V7 STI LTD code GDBB4JH. It has spec C engine but VF30 turbo.
The site also gives all other engine code (GC, GD, GH etc) I believe also legacy. Only in Japan Official website. Not in the Gobal site.