As per FAR 91.119, "... over any open air assembly of persons...", it's 1000' above the hightest obstacle within a 2000' horizontal radius.
Speed would be 250 KIAS, unless your manuals prescribe higher. For example, 300 KIAS is listed in the T-38 flight manual, so that's what we use.
Now, anyone organizing a flyover should have an FAA waiver for faster and lower. Not hard to do. I've done it with only 10 days advance notice and a lot of "Pleases" on the phone with the FAA FSDO.
But, any flyover worth doing should have the waivers in place.
Now,... even with those waivers in place, the USAF makes it difficult to go lower and faster: we have to get further permission from our chain of command to go "lower and faster". Is that bureaucracy also found in Naval Aviation these days? I'm hoping you guys have an easier time getting it approved than we do.
Also, how many passes are you allowed to do?