Rotary phase converter

Hi all -

Are rotary phase converters compatible with equipment that also
runs other systems (such as coolant pumps, brakes, CNC controls,
etc) off of the 3 legs,? Would the phase converter be trying to
start and stop every time the spindle motor was powered on and
off, and in doing so affect the other systems? I've never used
one, and I'm trying to figure out how and when they "self-start".
Can someone please explain? Also, can I run a 5hp motor at 3hp
with a 3hp VFD? The Hitachi literature warns against running a
motor rated higher than the VFD's rated HP, but I can't understand
why.

TIA,

Carlos Guillermo
VERVE Engineering & Design