Good read there Kenny. Sorry I cant give you advice on what to do or how cos my knowledge is limited to basic stuff regarding mods. Nothing compared to what some of these guys are doing nowadays.
I guess youre going to get all the block, internals sorted out as the main project first.
Then think about the stuff like injectors, fuel pump, headers,zorst, new turbo, FMIC, filter/airflow, ECU.
I think my old STI was running high 300s, maybe low 400s and all I did was
Injectors
Headers (equal length or almost equal length)
Fuel pump
Oil pump
Decat
49G turbo (pretty laggy and had to be worked on boost)
FMIC
Remap
Hope this helps