Personally.
I had the same dilemma a couple of years ago in my rs.
No point in chasing power in an N/A as everyone else has said.

Personally, cap your spending on the rx at $1k.
That will get you rear swaybar, springs & a decent set of pads + fluid. Also youll only need a 2 1/4 inch system for exhaust. That will give it some poke n burble.

These alone will transform the car into a fun car to scoot around in, plus it will look and sound good.

Dont be to focused on a wrx just yet, learn to drive the pants off this thing first then when you add some hp to the equation later on, youll have:
a. An appreciation of how quick it actually is.
b. youll know what & how to drive the car :-)

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2016 Subaru Outback - Work Wagon
350NM of CVT Goodness
Pit Crew, shit talker.