>>/963/
Are you synced with the PTR? That makes your four client.db files about 40-50GB now. The internal backup is basically just a copy of your 'install_dir/db' folder, which is:
The four client*.db files.
256 'fxx' file folders under 'client_files' folder
256 'txx' thumbnail folders under 'client_files' folder
>>/974/
Not much yet. Everything at the moment is here:
https://hydrusnetwork.github.io/hydrus/help/client_api.html
You can queue up URLs for download and fetch simple searches back, and files/thumbnails.
I hope to keep expanding it, including eventual full session control so you can make new pages and so on.
>>/977/
Giving them new names should do it. The basic 'new defaults' overwrite I use in my update (whenever I say 'rolled in a new blahbooru url class' in a changelog) works on name.
>>/983/
>>/986/
Yep, mostly you just have to wait for sync. It'll take a couple of weeks, and you need to have an SSD with 50GB of space. As long as your files are 'popular', the same as those stored on the big boorus and other gallery sites, you'll see the tags given to them by other anons on hydrus.