That's a pretty good deal on that Teco. I need a new VFD myself--my bandsaw ate the Hitachi I was planning to use on the mill (didn't hurt it, but it is now installed to drive the bandsaw). The other VFD I think about is a Delta, just because they make cheap drives with provision for spindle position sensing. That's helpful if you ever want to do a tool changer for a taper that has "ears". There is a note about it on my belt drive page:
CNC Cookbook: Mill Belt Drive, Pt 1
This Teco is sure a lot cheaper though, and you'd never need to index the spindle for an R8.
Where are you buying your Marathon motors? I would like to put a 3HP onto my mill when I do the belt drive just because it's a little extra margin if I am outside the power band. The mill doesn't need a full 3HP when you're in the sweet spot--not sure it's a good idea to try to use all of 3HP on one of these, LOL. OTOH, a big face mill sure soaks up some HP.
Best,
BW