I’m a bit nervous they’ll hum, that I’ll need to spend a lot of time and money repairing them, and that they probably won’t work so well when I use my system to play movies, which I will certainly do at times.
Old (vintage) stereo, like old (vintage) automobiles generally need repair sooner than later. And if you are not mechanically inclined, you will have to rely upon someone else to fix it. There is nothing wrong with used. But be aware of the age of the piece. If it is 20 yrs old or older it most likely needs capacitors and a good cleaning. I have bought a lot of used equipment but 10 yr old equipment is my limit on age.
As to the hum, that is usually caused by a ground loop and can happen with any system. Its more dependent on your electrical system. They are usually remedied with a little expense, often a 2 prong AC adapter.
As for movies, there should be no difference except instead of having 5 channels, you have 2 channel stereo sound. Now if you are trying to incorporate a 2 channel stereo with a HT system, that is usually a bad idea. Been there and done that. Two channel HT is fine with me