Unfortunately I've never used Gallery, so I can't offer any advice. There are some other
gallery add-ons which might be worth trying. It's possible to roll your own using
MIGX, but that might be a fair amount of work depending on what features you need.
For search, there's another extra called
AdvSearch which does work with TV content.
As far as documentation for properly configuring a media source when MODX is installed in a subdirectory, that post I linked to above is the first time I've seen it explained. The extras which get the blame for not working in such a scenario (I'm thinking of phpThumbOf here) aren't
causing the problem; they're simply not robust enough to
correct the problem when they're confronted with it.
I agree though, it's frequently a source of headaches for people. I remember being confounded by phpThumbOf not working when accessing a site via a URL like
http://somesite.com/~user/ on the first couple MODX sites I built!