I love 7speed. Can go with a freewheel, on a classic hub, like a Phils, or a cassette with a spacer, on a modern wheel, and it all works fine. I've run both in the same day, and not had to touch the RD adjuster.

Cheap Shimano 7sp freewheels, a Nashbar 7speed cassette, and and now a Shimano HG50 cassette, and have never had any issues. Back up, I did have an issue with an IRD 7 speed freewheel, that needed frequent kerosene flushing, and a dab of 20wt.

I've run down tube and bar end SIS shifters only, with vintage and current Shimano SIS capable derailleurs, with no issue whatsoever.

Some of the more modern stuff gets complicated, 7 speed is not. Only wish it was easier to come by shift levers.

Just do it.