200kw atw from an original 16yo EJ20 block? lotta money there so I hope you've got a big wallet or a really good job, you can expect one or all of these things to shit themselves continiously...... block, clutch, gearbox, axles etc etc, you'll really need bigger brakes unless you already have 4 pots, better off saving the money and waiting for a 99 2 door or 00 4 door STI or even better an 02 STI with Brembo's and a 6 speed and big top mount already fitted for less than you'll have to spend on your 98 WRX shitter.

EJ 207 with decent pistons new oil pump, water pump, belt kit, gasket kit, lets say $4000-6000
6 speed to stop your butter Aus 5 speed dying with decent clutch $4000-6000
Injectors 2nd hand $400-800
Turbo $1500new.
3" turbo back $600 rubbish to $2,000 recommended Butler
Top mount, brackets and new clutch master 2nd hand probably $450
Fitting, $3000-4000.
Computer 2nd hand $1500, every mod you make another $300-500 to re-tune.
Bigger brakes $600-1400
Then all the other bullshit like R180 rear end over 1k
So to add it all up, fuck your 98 off for 4k and buy a Bug Eye STI for $14,000 and save about 10k

__________________
Beaten up old 98 Gen 2 Liberty, 13.0, stock V3 STI running gear.
07 Transit motor home
69 VF & 70 VG Valiants needing full restoration
Yamaha Zooma 50cc rocket hopefully going with the Transit.