Collector sites
Below is a list of each site Luster can collect from, and any information particular to it.
Rule34
Rule34 supports most tags and, as far as I can tell, does not have a tag or page limit for what it will return. Will make up the large majority of your results.
Danbooru
A very mid site. As it is now impossible to get a Gold membership, all new users are limited by a max of 2 tags per search and a page limit of 1,000. You can review the limitations of a free account here: https://danbooru.donmai.us/wiki_pages/help%3Ausers
Gelbooru
Seems to have every tag, for better or worse. No account required and from anecdotal experience, decent quality.
Luscious
Great for manga and curated albums. Needs an auth cookie for best results, which can be found in the dev console of your browser.
Nhentai
A large repository of Doujins and the like. Requires you to get both your browser cookies AND user-agent to work properly. If you use something like Komga to manage your Doujins, I would suggest enabling zip_albums in configs and del_files if you only want the CBZ. If you are using zip_albums, metadata is automatically added from Nhentai into your CBZ.
Xbooru
It do be another image board site.
Konachan
An image board for anime/manga wallpapers.
Yandere
OMG AN IMAGEBOARD.