1900 or 2300 will be fine, only other option would be a Whipple. Some say the 2300 works well, others the 1900. My opinion is that if they can run 1900's on 6L's and bigger than its adequate for a 5.7L.
I run a Maggie 1900 and don't regret going with the smaller one. Makes plenty of power, runs fast times and throttle response is awesome.
Can do either. I would just send them to Higgins and either get him to port yours or exchange them. Plenty of people have gone the aftermarket route though (there's a set in the FS section that would work well actually).
Do you have a cam in it yet? I wouldn't bother with the heads unless you've got a decent cam or plan on doing it. If you haven't got either, then you're starting to look at 4500-5500 here already, in which case, I would just go straight to the blower and slot a cam in later, leaving the heads stock.
I wouldn't bother with the VCM box. A sealed pod tends to work well with blowers but IMO the difference between what you have now and other options is more the 'icing on the cake'. Put the blower on, see how it goes. When you crave a little more, then play with the airbox, throttle body, cam, E85 etc etc etc