Vacuum Booster or Not?

I would go with power brakes when upgrading to discs on a daily driver.
Discs require more effort than drums so you will have to get even bigger leg muscles if you go the manual disc route.
My '65 Valiant has non power Kelsey Hayes discs from the factory. They do a good job of stopping the car but the pedal requires a lot of pressure so you don't get the feeling of having good brakes until you really step on it..

As much as I love the Kelsey Hayes brakes I might go for the later A-body single piston discs and BBP conversion if I was to upgrade a car that didn't have them allready. A much simpler design that works at least as well. The four piston KH calipers work good but have alot more moving parts and so are more complicated and expensive to work on.