pnwc, welcome to BF and specifically C&V. You've come to the right place.

Lots of questions and I can't answer them all. But I can tell you it is not easy to find Uniglide cassettes. You are better off going with a 7 speed Hyperglide cassette, SRAM, Shimano or Sunrace. There is a spacer made to fit behind 7 speed cassettes to be used on a 130mm spaced hub.

Friction shifting gets more tricky the more cogs you have in the rear. You'll be fine up to 7, 8 okay, 9 is a challenge but is possible.

You can try the old chainrings, but if you are going to a new cassette and chain it might make sense to use new chainrings as well. Cogs and chainrings tend to "wear" into the chain. If you change one thing sometimes there are shifting challenges which didn't exist in the past. By replacing all three at the same time those challenges aree usually avoided.

Best of luck on your project! A rule of thumb here is to always post pictures.