What mods do I need to make around 300whp on a 2022+ WRX?

Start with the tuner and intended fuel, not a shopping list. Wheel-horsepower readings vary with the dyno, conditions, correction method, and vehicle, so the same displayed target does not define one universal hardware package. Give the tuner the exact car, transmission, available fuel, reliability priorities, emissions requirements, and budget. Ask which intake, charge-air, exhaust, and fuel-system parts—if any—their calibration actually supports. Do not assume that a named stage, MAF diameter, or another car's dyno sheet transfers to your combination. Ethanol-capable setups and pump-gas setups have different fuel-system and calibration needs, but neither should be specified from a generic horsepower number alone. Confirm local fuel availability and test the fuel you will actually use. Torque delivery matters to the engine and transmission independently of the headline horsepower number. Agree on torque limits and logging/review steps with the tuner, then budget for installation, maintenance, and contingency as well as parts.