People will want to download chicks or parts of the torrent, you should leave them separate.

Jpeg is already compressed, so compressing them again won't do anything but make it impossible for people to selectively download just the image/folder they desire.

Metadata on the other hand sounds like text files, which compress very well. Wether the space savings is worth it is hard to answer without more info. I'd personally lean towards not archiving it.

Only if you can achieve significant compression. 15% or more.

Yes, you can, I would say that it would be good to deduplicate files first.

Also put a txt file with locations and file hashes in torrent, it could be usable if some valuable files were lost in the future due to seeders being inactive and torrent becoming dead, to make .torrent file smaller you would choose a bigger piece size, but in this case users would have to waste additional traffic if they are downloading only files they choose.

It would be nice then to have BEP-47 support for file alignment, but this comes with many padding files locations in torrent's metadata which makes it bigger.

If you have a big nested structure of folders, then every file there would have something like this info in metadata: folder1/folder2/folder3/file.jpg

All of these problems could be solved, if you're choosing format to BitTorrent v2 only while creating the torrent, but keep in mind that it won't work with Transmissions and uTorrents. qBittorrents are working.

You could choose a hybrid, but it makes torrent size a lot bigger.

So overall, bestly you would choose v2 or hybrid (with hybrids sacrificing torrent's size greatly, but providing your users with file hashes, deduplication and reduced bandwidth), or make at least a v1 torrent, optionally in a client that supports BEP-47 after deduplication and adding .txt

Leave them as is. I hate having to deal with archives inside torrents unless there's a very good reason for them.

Why not both?

I'd put it all in a single archive.