Welcome to the wrx community mate, your mods list will definitely sharpen the car up significantly and also provide the much loved boxer-rumble.
The best advice I can give is to forget about a target power figure. You might end up with a high-power car that drives like crap because the power only comes on late in the rev range. It is much better to have a tune that has a greater area under the curve, more-so than just focussing on the final figure.
Choose your tuner before choosing your mods and then discuss with them what you want the car to achieve, then trust their advice on what you will need to meet them.
Plenty of threads on here re Perth tuners so have a search.
All the best!
Tom

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Now handles like a cat on carpet