Yep...

I have a bike that squeaks during shifting... Friction so I can usually find a quiet sweet spot. I need to tear down the rear derailleur sometime. Not a big deal. Pull it apart, clean, add a little oil.

As far as the rusty chain. For occasional use... just break it loose, oil, and ride.

If it is deep pitting rust, and you wish to use the bike a lot, then replace.

If it is light surface rust, don't worry about it.

Keep in mind chain stretch. Usually measuring > 1/16" per foot is considered worn out, and should be replaced.