am looking at milling MDF and plywood, do I need the extra RPM?
Unlikely. The “correct” RPM is calculated using the bit diameter, number of flutes, and the feedrate. I cannot think of one time since I purchased a variable speed router, I’ve run a CNC job at full RPM (30,000).
Can you control the RPM of RT700 with software? Or is it manual with the fingers only?
Fingers only. I think I read somewhere there is an add-on board to allow the RPM to be set via g-code, but my searching is not turning up the reference. Many people add a relay switched by the control board so they can use g-code to turn their router/spindle on and off.