No, the pedal would be stiffer without vacuum.  What brakes do you have on the car?

Did you adjust the booster output shaft to fit the master cylinder?  Are the rear brakes adjusted?

What booster is it?  If you got it from me, I adjust every one of them with a jig I built.  They all come WAY OUT OF ADJUSTMENT and will result in a very low pedal if you just bolt it on without adjusting it.  Yes, remove the mc.  You don't have to take it all the way off, and might not have to remove the hardlines if you built in a couple of loops for ease of movement.  Just remove the two nuts and pull it out about 1-1/2" so you can get to the adjustment on the shaft.

Easiest adjustment method is to extend the rod until the MC rocks in it when you push the mc up to the booster.  Then back off a tiny bit and retry the mc to see if it rocks.  Once it doesn't rock, you can bolt it down.  A half a turn moves it farther than you would think, so go in small increments.

What booster are you using?

That is a Fox Mustang booster.  The ground support booster just happens to be the same size!  What spacer?
No matter what, the end of the rod needs to be within about 0.010" of touching the piston in the mc.  The black boosters have their own jam nut.  The cardone ones do not have a jam nut.  If you added some kind of spacer between the MC and the booster, the rod will have to be longer and you need to be sure the threaded part of the adjuster is in no danger of coming out too far and falling out of the shaft. Some red loctite will hold it, assuming you have enough depth of thread engagement, but I have never seen one come "unadjusted" once it was set to the proper depth.

Perfect !