I'm building a dust collector and need a somewhere in the neighborhood of 5hp or so to run the impeller. I've looked at a bunch of specs on a bunch of websites, and come to the conclusion that either I don't know two cents about motors, I don't know what I'm looking for, or I can't see through the marketing speak...

Does anybody have any pointers if I state the following:
I have up to 50A of 220V single phase.
Sheave bore is 1-1/8".
RPM is somewhere in the 3450-3600 range.
Probably direct drive and vertical mounting (motor on top).

I don't know what to think, because I've seen a price ranging from about $100 to about $1000, and I really can't tell much of a difference. Common sense tells me that what I'm looking for should be rated for at least 21A for continuous operation otherwise I'm looking at peak numbers.

On the safety side of things, I keep reading about magnetic switches, though I'm having a hard time finding anything to handle a motor over 3hp. Does anybody have a good pointer for that as well?

Lastly, is there any sort of balance or vibration switch/cutout device available for added safety? I'd hope I don't cause anything so drastic as to have a 5hp motor come out of a mounting and attempt to walk around the room, but I figure there can't be any harm in asking...

Thanks in advance!