Yeah, absolutely. You have to book a ROZ up to 16,000ft just to fire a 81mm mortar, never mind throwing a payload into orbit. Firing HIMARS (the truck based version of the MRLS) involves putting a set of goalposts a mile either side of a target, drawing a line from there back to the launcher (max range, 250 miles) and clearing everything out of that airspace from the ground up.
I don't even want to know the size of the ROZ you'd need for a multi-stage rocket launch, or back when they'd throw STS up, with SRBs and ETs coming down and a potential un-powered shuttle divert.
Yep, I don't know this myself, but apart from the flight space they also close navigation in a given zone. Because boosters or first stage fall back in the ocean, and there's a risk of a malfunction during the launch, so the whole rocket can fall back.
That, I didn't know. I take it you guys don't like doing things like that on home soil?
I believe it was once considered to launch from France (to be verified!), but Guiana has been chosen because it has lots of qualities (a part of Guiana is french): it's near the equator, so the same launcher has extra capacity because of this. Another advantage is that the ocean is on the east side. Rockets are generally launched eastwards, because Earth rotates from west to east, and the launcher benefits from the extra speed. In case of an early failure the launcher will fall back in the ocean (or boosters anyway), which reduces the risk of casualties. If we launched from Europe that would be very complicated, we would probably have to launch westwards like Israël does to avoid that kind of risk, but then it reduces the launcher's capacity. By the way, Russia is at the East of Europe, and in the end of the cold war it would have probably been a very bad idea to launch towards east from Europe.
Now there are some constraints because of this. The launcher parts are made in Europe and then they are shipped to Guiana to be assembled there. Those are a lot of extra-costs in the end. That doesn't seem very important, but because of Space X performing launches at low cost, Ariane 5 has suffered a lot from this for a few years (not as much as the Proton though), so it also has its drawbacks.