Essential/best bang for buck mods are a flash tune, intercooler, 3" downpipe + exhaust system, l.s.d + clutch and single mass conversion while you have box out.
Turbo solenoid brand depends on who's tune you will run also worth upgrading the c.b.v and wastegate actuator.
This will net you at least 185+fwkws that will actually be usuable with the LSD
Any expected power level over 230kws requires a bigger turbo than the stock k04 and enters the realm of cracking cylinder liners. This can be mitigated with the available shim kits but costs increase greatly for this power level and you'll struggle to actually use the power on a street car.
With the new gst rules Jamie @oem denied is pretty competitive on price and his knowledge of the product and customer support is worth taking advantage of.
I do lots of work for the local xr5/RS crowd in Canberra and I daily drive a C30 with k16 and the entire elevate Catalog plus a quaife and twin plate Xtreme clutch.
I helped Danilo build the car and we are currently working on a 1963 Amazon wich we have fitted with the duratec/Whiteblock.
https://ozvolvo.org/discussion/3102/danilos-2008-t5-rdesign-volvo-c30/p5
https://ozvolvo.org/discussion/5572/1963-volvo-amazon-t5/p18