Starting to get interested in tubes

Your Nova 300 is a better choice for use with electrostatic speakers than any tube amp! Why? Because all electrostats have a wild impedance curve that goes from high to low (1 ohm above 10 kHz). This is a brutal load for any tube amp. Add in the fact that tube amps tend to have relatively high output impedance and can't deliver much current to a complex load. If you must have a tube component just get a nice tube preamp instead! 

If the Manley amps have an output impedance of 1 ohm or more they will not have a flat response into the varying impedance of an electrostat. They will instead follow an electrostat's impedance curve. 

Yes, you can use an autoformer on each of the Manley mono blocs. This will solve the impedance matching problem.