Visas - The UK will want visas for some of the East European countries, when it wants to restrict unskilled workers or those that have no prospect of getting work. But it's in everyone's interest to keep this as simple as possible
Trade - I don't buy the "We must make an example of them" argument. Sure, if we were a minor country, perhaps. But with an economy the size of the UK's it would be commercially extremely damaging for the EU (as well as the UK) to take this attitude - they won't
Migrants - OK, so you think the French Government will jeopardise their country's own security arrangements by losing their police presence at exits in the UK. Suicide for the government if there's another atrocity there, and one or more of the terrorists come from the UK (they're already having to deal with our anarchists over there)
EU citizens - not true that it hasn't been spoken of. I've heard from several Brexit sources that it would be ridiculous to send anyone home - I don't think even Cameron is claiming this (give him time) which says it all
I don't think you're scaremongering, Supergod, and you have a point that the Brexit crew need to address visas from an administrative point of view. But the other stuff will not be an issue imho