honestly, alot of people have done wrx swaps. I would think its the best way to go if you opt not to build up the block. In the end...
If you wire in a wrx ecu, and basically make your car a old school wrx. It will be the more reliable power adder you could do since it is factory turbo.
About the forged internals: I honestly think that would be overkill unless you want 400+hp on race gas. i've seen a wrx run low 12s (i'm talking almost 11s) on 100oct, boltons and a ecu reflash.
i'm not saying don't go forged, because if you do build a 2.0l it might be able to handle a few mistakes (ie bad gas or bad tuneing) better then a cast motor.
non the less, you have alot of options ahead of you. I suggest you read read read about the wrx motor and make sure thats the way you wanna go.