Seconding the recommendation above. The OEM shifter is a great start, but adding a few more bits makes a HUGE difference for low cost:

• Perrin Brass Shifter Bushing - gets rid of that rubbery slop for cheap.
• Nameless Performance 4 inch Muffler Axleback Exhaust - gives you that subie rumble without the cost of a full catback. tbh these are super safe mods that dont touch the ecu so youre good!

Yo, congrats on the new ride! Honestly, for the best bang for your buck while keeping that warranty safe, I would suggest starting with the Subaru OEM Short Throw Shifter. It is a factory part so the dealer wont give you grief, and it totally fixes the stock rubbery gear feel. For sound, definitely look at a Remark R1 Spec Single Exit Catback Exhaust. Since it's post-catalytic converter, it doesnt mess with emissions or the ECU tune, so it's a safe bet for daily driving. Technical-wise, you're spot on about the AOS. I'd basically always recommend the IAG Performance V3 Street Series Air Oil Separator. These FA engines are direct-injected, so oil blow-by can lead to nasty carbon buildup on your valves... which is a nightmare later on. It keeps the intake tract clean and the engine happy long-term. Plus, most shops see an AOS as a reliability mod, not a performance one, which helps keep the warranty vibe chill. Peace!

Be careful about any performance mods that require an ECU tune because dealers can use that as an excuse to void your powertrain warranty if anything goes wrong. Even simple stuff like an intake can sometimes cause issues if the engine leans out or they see youve messed with the software. Anyway, congrats on the new WRX!! Honestly one of the funnest cars out there. For your situation, I would suggest focusing on the mechanical side first. I put a short throw shifter and some bushings in mine and it literally transformed the driving feel... way less rubbery and much more precise. A cat-back exhaust is also a safe bet since it doesnt touch the catalytic converters and usually wont mess with your warranty. Plus, an AOS is basically essential for keeping these boxer engines healthy long-term imo. Those are definitely the best bang-for-your-buck mods! What color did you get??

Building on the earlier suggestion, I'd suggest looking into drivetrain and braking feel if you want to stay safe for warranty reasons. Since these dont touch the engine software, you should be fine. Keeping things conservative with mods is usually best because I dont want to deal with dealer headaches later tho.

• Perrin Pitch Stop Mount: This helps stop the engine from rocking during gear changes. Pro: it makes the car feel way less sloppy. Con: you might hear a bit more engine noise in the cabin.
• Cobb Tuning Pitch Stop Mount: Similar to the Perrin but some prefer the finish. Pro: solid aluminum construction protects the car from stress. Con: it is slightly more expensive than basic options.
• GrimmSpeed Master Cylinder Brace: This is a reliability must for the brakes. Pro: it stops the firewall from flexing so the pedal stays firm. Con: it takes a bit of patience to bolt in since space is tight. I would suggest checking with your specific service advisor first. Some are way more strict than others about accessories... just gotta be careful.