Hi Natalie,
I can probably help you out with a few of these questions, mainly those related to the motor.
The answer regarding the servo motor...yes it should fit. if you can fit a clutch motor, then you can fit a servo motor on a manual machine.
Is it hard to switch? Not at all. I just converted mine to a Ho Hsing MJ Series 4 days ago...the best change that I have ever made. Your belt size may change depending on the size of the servo and positioning.
There is a way to make your clutch motor perform differently. This requires you to play around with the screws on the motor and the pedal because really it all comes down to setting sensitivity. You may want to get a smaller size pulley as well. I have an 80mm on my clutch motor...you should be able to get something less...maybe like a 40mm.
I don't think I was too bad myself on a clutch motor but it depends on what you are sewing. If you are sewing upholstery covers, then a clutch wouldn't be too bad especially if you are doing lengthy straight stitches. If you are making bags...wallets, etc, and you require precision, I would then recommend a servo with speed control.
If you are going to go down the track of getting a servo (which I would recommend) and you are sewing through heavy materials, please make sure you get something around 600w - 650w. I go through leather / fabric / glue all at the same time...no problem.
Good luck with all!
Chris