VF35 and VF34 are both based on a vf30. VF35 has a smaller exhaust side improving spool but slightly dropping peak, VF34 hs a roller bearing core but retains same exhaust.
35 and 34 have pretty much same spool but vf34 tends to have 10bhp ish more peak, cos of its better peak tends to hold its value better second hand as well as being bigger cost from new
Pretty typical up grade path, as long as you find decent second hand parts you'll be fine.
brakes would be a good upgrade before though, on a wrx they aint great
When you up the boost you need to adjust the fuel and timing or you risk it self destructing.
Stay well clear mate and if you wanna up the power get a proper remap
ah that might make a difference then lol.
im not 100% sure but cant think oif anythign different on a wrx cluster comapred to a gl cluster, if its cheap enough might be worth a punt