I'm at something like 330hp/385tq on the dyno, and there is no way forward now without a full turbo, motor and tranny build. So, my advice comes from my car & experience, and you'll obviously have to talk to a tuner about getting to 500 hp at the wheels.
All that being said, my car (a 2013 WRX hatchback) realistically struggles to handle the power level I'm at now on the stock clutch, brakes and tranny (particularly the rear diff), and I barely ever get into fully boost below 3rd gear. A lot of this has to do with the rear diff and transmission in general, so I would strongly suggest you drive/ride along with a car that's at the 300 hp/350tq mark, and see if that's enough for you. The jump from there to 500hp is a big one. I suggest this, because you're going to be in for a serious bill once you build the motor, turbo, clutch, tranny, fuel system, and other supporting mods to get there (brakes, suspension, cooling, tires... the list goes on and on at that power level). Only a tuner can get you the real info you need to make that power.
Now, assuming you have the cash to get there (I'd plan on $15k
minimum to do it right, which it has to be if you are going to DD it - and you seem to understand that), awesome. Do it and enjoy if that's how you want to spend your money (and make sure you show up at my place to give me a ride!). And plan on a motor rebuild every 50k, and you should get your fun and money out of it. However, from my point of view, the sweet spot for power/money ratio for these cars staying primarily stock is stage 2 with a EBCS and a good protune, with small supporting mods (all done for around $1k). All easy modifications, and it really opens up the car. Past that, I think you end up changing out so many parts that you might as well have started with a different platform. If you are serious about it, I'd suggest starting with an STI over the WRX as well.
So, if you are serious, here's a build that he daily drove. Make sure you read the whole thing:
http://forums.nasioc.com/forums/showthread.php?t=2078765