I am fairly clueless about it, please forgive me if my questions are
completely stupid.

-The current motor is 1075 rpm 4spd (direct drive), do I need to go with a
4spd motor replacement or a motor with smaller # of speeds will do. I cannot
set the speed with the thermostat, so I presume thermostat sets the speed
internally, based on its own built-in rules. I am guessing then that less
then 4 speed motor will not work or will not be as efficient.
-The motor is 1/3 HP, does it make any sense to go with a slightly more
powerful motor, i.e. 1/2 HP? Any advantages/disadvantages?
-The motor has an external capacitor 5/370. Can I get a replacement motor
with different capacitor's parameters, assuming all the rest of the motor's
parameters and dimensions are the same. Will it work or the motor must have
exactly the same capacitors.
-What's a good and inexpensive place to buy the motor on the internet? What
should I expect to pay for it: 115V, 1/3HP, 60HZ, 5.8 AMPS, 1075RMP 4SPD

Thanks a lot for your help