I'll try to summarize my thoughts to keep this succinct...
As mentioned, this has been discussed and attempted for decades. Back in the early 2000s there was a crew of guys on this forum pushing the EA82T. At that time the turbo EJ was still pretty new to the U.S. and the cost of entry was too high for most of us cheapskates. Not many people had the gumption to invest in an unknown, undocumented EJ swap. People kept pouring time, money and ideas into the EA82T and since I was keen to replicate their success on my EA81T, I paid close attention. From memory, not one of those cars has survived today and is still running.
Contrast that to the first few EJ-swapped EA82s and they're still out there. Hell, my RX-RA that @suberdave built back in ~2005 is still on the road with the same engine that was originally swapped into it 16 years and three owners ago. Try making 260 chp for 16 years on an EA82T... Hasn't been done yet, probably won't happen until somebody creates new, redesigned head castings. The bottom end should hold up to quite a bit of abuse, but the pistons and heads crack, HGs aren't up to the task and the stock ECU is closer to an Atari than smartphone.
To do what you're describing and keep the engine reliable (we're taking cost of acquisition/hard parts/labor/machining/and ECU tuning labor) you're probably looking at a $10,000 investment. The custom parts will be more expensive because they'll all be one-off parts. You'll want to pay someone to tune it, since there are no base maps for this engine. Now, an EJ? If you've got the coin you can bolt in 300 chp, leave it stock and be able to enjoy it for the next 16 years vs. the next 16 days (until the EA82T blows up...).