First off, go with the 3ph in if you have it, then you won't have to derate the VFD, hp wise. The most important thing on a VFD is not to exceed the rated current. If you have a 1.5hp motor the 3hp should be fine. Flux vector is a way of controlling the speed in lieu of a feedback device which is a sensorless VFD, usually if you have a digital tach or encoder you can obtain the type of VFD that operates in the torque mode and accurate speed control is possible, If you operate a sensorless vfd, try not to drop down in rpm too low with high loads as you will probabally find it will bog down. Most VFD have the ability to just add a pot for speed and provide a voltage out to feed the pot. Make sure it has an external mode as well as keypad setting.
You can get sophisticated type that have auto tuning and will run your motor through a series of tests and automatically plug in the parameters.(Mitsubishi for one).
If you have a 4 pole motor (1700+ rpm) then you can usually set the max frequency to 120hz and run up to almost 3600 rpm, This is as long as the motor is well balanced, the limiting factor is if you start getting vibration at high rpm.