Welcome to AFM!
1. A Typhoon intake is okay, they are China made Edelbrock copies. They usually need some porting/cleaning up to get them to flow where they should. I would get different intake, I think $425 is a little steep.
2. The way a camshaft idles is one of the many factors that goes into selecting a camshaft. There are a few guys that can make you a really good custom cam, it isn't nearly as expensive as you might think. As far as off the shelf cams, Lunati and Comp would probably be able to recommend a good one for your setup. Speaking of valvetrain, do you already have roller rockers? If you don't, plan on getting them. Also, the current valve springs may not be up to the task of a different camshaft, be sure to check that out before finding out the hard way. As for hydraulic roller lifters, these are the best bang (er... not bang... bad term here
) for the buck: Howards Cams 91168 - Howards Cams Street Series Retrofit Hydraulic Roller Lifters - Overview - SummitRacing.com
3. Assuming the pistons the motor has are flat top pistons, you're probably around 10:1 to 10.5:1 static compression ratio. This isn't too high, pump premium will work fine with a good cam. If you do get a different camshaft though, you need to pop off the heads (well, at least one) and check piston-valve clearance. Another thing that's really sucks finding out the hard way.
4. A quality port job will probably help those heads out.... I would.
5. Injectors: Put it together with the stock 19# injectors. When they prove themselves inadequate (which they probably will) decide from there. It should run fine with the ones off the 5.0. If/when you get heavier injectors, you will most likely have to get a better fuel pump.
6. I'm not 100% familiar with those heads (I don't think so anyway), so I can't really make a good guess. But if I were to... If everything gets done right I could see 365HP.
I hope this helps, and good luck!