I am the proud owner of a 2002 Acura RSX type S 2.0 k20A2. I won't lie to you, she's in rough shape.
Before I bought this RSX, I bought another with the intention of restoring it. The previous owner of that car smashed it into a pole and didn't want it anymore. I got it for a great price, but once I started tearing it down I found that the frame was badly damaged and not worth saving. So I gutted everything, engine, tranny, wheels/tires, suspension, dash, column, steering wheel, seats and more. It left for the scrap yard as basically a shell. Long story short I have a garage full of stock RSX bits including the engine which is still in good shape.
Enter this RSX and current love of my life. She was neglected by her previous owner. She's got rust in all the wrong places, a bumper that's held on by zip ties, big dents, long scratches and an engine that's on its way out. But I love this car and will not let it die. Far from it.
The plan is simple, rip out the worn out engine in there, rebuild the engine in my garage with upgraded components, fix the body, slam the new engine in with a nice paint job and boost the heck out of it.

Okay, so it's not nearly that simple, if it were I wouldn't be here seeking advice.
I plan to do most things myself, I'm a level 2 apprentice with 4 years experience in the automotive trade and I have torn engines down before, but never a honda engine and never with anything but OEM parts.
At the end of the day I'd like this car to be street legal and have 350-400hp that I'm not going to be afraid will explode.

bottom end:

The stock bottom end just is not strong enough to withstand boost and the horsepower I want, so I know it will need to be upgraded in a big way.
-Pistons: Another tech said that forged aluminum is best due to the light weight
-con-rods: A strong forged steel probably
-Crankshaft: this one I'm really not sure about. The advice I have received so far is that anything but a very strong billet steel crank will just snap under boost. Is there any truth to this?
-Bores: Will the stock block be strong enough to handle boost or will sleeves be necessary?

top end:

In the interest of not completely breaking the bank I'd like to keep the stock head. I have never done any upgrade work to the cams though, any suggestions for adding some strength against that demon valve float and maybe getting a bit more power out of the timing would be greatly appreciated.
Or if the stock head won't cut it, any suggestions on what to replace it with would also be great.

Intake:

Probably the bit I know the least about. The horror stories of people paying for aftermarket turbo setups only to end up losing power by having too much restriction scares me a little. The only advice I've found so far are for ready-made kits you can find online. Is buying a kit thats already put together the right move or should I be looking at building it myself? I'd rather not get some garbage parts for too much money that I can't return, but I also have never put together a turbo system before.

Exhaust:

While I know how to weld to some degree, I'll probably have a muffler shop put that bit together for me. In a perfect world I'd have a custom header and pipe welded together for me, but is there any other option that might be a bit more cost effective?

Thanks in advance

 

Research, loads of people have built turbo K20s, see what other people have done for given power levels and what worked for them. The answers to all of your questions are 100% dependent on how much power you want to make. The parts needed for 300whp are wildly different than the parts neede for a 600whp build. The K20 might be one of the most documented engines in existance, almost every possible build has already been done multiple times.