Can’t answer your questions directly as my only experience is with a VFD on a 1HP motor (and it works fabulously with speed control). 

One of the things I’ve read that makes sense to me (especially when looking at used tools) is that used 3-phase tools seem to sell for cheaper than their single phase counter parts. I’m told/am guessing that this is due to a smaller pool of buyers. That said, the price difference may be significant enough that adding the cost of a solid VFD may still leave the tools cheaper than its single phase counterpart. It seems 3-phase tools are also beefier and more solid…that may be a good thing or a bad thing based on how much room you’ve got and how you plan to move them. 

Again, I’m limited in my VFD experiences but based on what I’ve done to this point, I’d be actively considering used 3-phase tools and a VFD going forward…especially if the price is right!

I’ll be following to get info from those with more experience on the matter!

Ryan/// ~sigh~ I blew up another bowl. Moke told me "I made the inside bigger than the outside".