Commentary from the voice of experience with the Vortech.
1. Agree, if you want 500rwhp, you should replace the bottom end.
2. Crawford plenum and new lower intake will be good for you. For the same price, the new Kinetix Intake Manifold would be a little better. Specifically designed for FI applications and shown to create a little more power than the upper plenum replacements.
3. A moderate step up would be to replace the cams, but they do make a big difference on an FI car. For FI applications, I'd recommend Nismo, Tomei mild grind, or the JWTs. I have the Nismos, but if I were doing it today, I'd buy the JWTs (they were not available when I did my build).
4. No TechnoSquare reflash. On a Vortech car, the flash will make it more difficult for you to tune with the Split Second box and R4 software. Only real gain you would get with a TS reflash would be to raise your rev limiter or to help handle bigger injectors if you go that way.
Based on what the little I can read from your post, I'd recommend getting cams, headers, and maybe the 3.12" or 2.87" pulley. Then shoot for low 400s. Anything higher than that is risking your bottom end.
So says the man tuned to 425rwhp and still driving his 17K miles later. :irock: