This site is a really comprehensive resource on gba and ds: http://problemkaputt.de/. Source: over 1 year ago

He has probably deleted that, well go to https://problemkaputt.de and redownload it. Source: almost 2 years ago

Nocash is responsible for a number of different emulators over the years, most of which include powerful debuggers. They've been quite useful for a lot of emudevs here (myself included). Source: almost 2 years ago

For documentation, Gameboy programmers seem to recommend "pandocs" and nocash tends to include excellent hardware documentation with his line of emulators (though apparently the gameboy emulator isn't as accurate as it could be). Source: over 2 years ago

Http://problemkaputt.de/ has a lot of docs for different consoles. Source: over 3 years ago

Usually the downloader you need depends on the website you want to download the images form. In general, here are some opensource ones which support a variety of websites: gallery-dl, ripme and various other ones on github. There for paid ones, there are Extreme Picture Finder and Bulk Image Downloader, which have easier to use GUIs and are properly maintained, but as said, they are paid. Source: about 3 years ago

Yeah, I found bulkimagedownloader ages ago but its not a free tool. Not sure of what limitations the trial have. Source: about 3 years ago