Introduction
Radarr is a movie download automation tool that ties together your movie collection, indexers, trackers as well as your usenet and torrent download client. It supports a wide variety of newznab usenet indexers, a number of torrent trackers, a handful of usenet download clients and a couple handfuls of torrent download clients. You can greatly expand the number of supported torrent trackers with jackett, a tracker to torznab proxy.
How Radarr Works
One of the most misunderstood mechanisms of Radarr is how it finds movies to add to your collection. It seems obvious to most new users, it searches for them. And if it isn't found then, it'll search later for them. Right? But this is not how it works. If you think about it, that sort of mechanism does not scale at all. If you search every day and have 10 missing movies, that is 10 searches. If you have 100 missing movies, that is 100 searches. If you have 1000 missing movies, 1000 searches. Every day.
Instead, Radarr does an "RSS" sync every 15-60 minutes which queries your indexers and trackers for newly posted content which lets Radarr cover any number of needed movies with just 24-96 queries per day. Your library size, number of movies that are missing or need upgrade no longer matter. Most of these "RSS" queries return new content... but with usenet, where reposts are more common, older content is fairly common, but it isn't as common with torrents. So a movie added to Radarr may never download if it never shows up as newly posted content on your tracker or indexer. So how can this be feasible?
When you're adding a movie you know can already be downloaded, you'll pick the right profile, root folder and monitor status... you'll check the "Start search for missing movie" box and then add the movie. This will add the movie and initiate a search, which covers the past and the present which let's "RSS" cover the future.
And the best part of "RSS" is that it is actually a search, but without any query parameters besides your indexer/tracker categories.
Indexers and Trackers
You will need to get your .nzb files from a usenet indexer and/or .torrent files from a torrent tracker. There are many public and private, well known and secret options available and I suggest /r/usenet and /r/torrents as good starting points for finding them.
But how do you decide, torrents or usenet? Personally, I'd suggest both. But if you want to go one way or the other, that is fine too. Torrents have the benefit of being very inexpensive, where the only real cost is a VPN to keep you safe. On the other hand, you'll pay a small amount for a few good usenet indexers and a bigger amount for a usenet provider or two... but you won't have to seed. On the gripping hand, having both setup means you get all the benefits of both.
Download Client
You'll need to pick a download client.
For usenet, this is very easy because nzbget and sabnzbd are pretty much the only reasonable options and they're both fantastic. Pick one or the other based on looking at their sites and if you like it, you're done. If you don't like it, try the other one. There are tiny differences between them, but they're both wonderful and you can't go wrong either way.
But now we come to torrent clients, and my opinion of them is that there are none that are as good as the above usenet download clients. I would start with qBittorrent which has been growing in popularity and seems to be actively developed. If that doesn't suit, I would try Deluge next. Finally, as an rTorrent user myself... I would try it last. And you should absolutely scour the internet for articles, opinions and comments about each one because they are all very different and some do certain things a lot better than others. And don't forget, extraction of packed torrents is an after thought in all of them.
Note: This guide is written for Radarr's Aphrodite branch, known as v3.
Library and Download Folder Setup
You've done the hard part, you've selected your download client and indexers/trackers. Now we move on to the next task, which is getting your library and download folder sorted out to be the best it can be. From a very high level, Radarr is going to need to be able to read and write to both folders. Your download client will also need to be able to read and write to the download folder. If you have an existing library of movies you're going to import, it will need to be in the right structure which is a movie.ext file in a movie/ folder which is in a folder of movies/, like movies/Movie Title (Year)/Movie Title (Year).ext. Ideally, the movie file name will also contain the quality/source (like DVD, HDTV, WEB-DL or BLURAY), edition (Theatrical, Director's Cut, Unrated) and/or -GrouP. All of this information is irreplaceable, it cannot be found any other way. So if you have that data, make sure it is in the file name.
Ideally, your download folder is on the same file system as your library folder. This will allow imports that move, like usenet and torrents that are finished seeding, to be instant and it allows hard links for imports that copy, like torrents that are still seeding. For moves, it saves time and io which most users won't really notice... but for long term seeding, hard links allow a library and download copy to exist without wasting space and the download folder can be a hot mess while the library folder is nice and neat. If you want to download to a different drive or file system, like an SSD, you can still achieve this by having your incomplete folder on the SSD, but your complete folder on the library file system.
I would also suggest separating your downloads logically, putting usenet downloads in one folder and torrents in another. And inside those download folders, consider category based sub-folders too. For example, /data/usenet/{tv|movies} and/or /data/torrents/{tv|movies}. I like to avoid naming the folders after the software itself, since I don't know what the future might hold where I switch from one to another and then end up in the awkward situation of using SABnzbd pointed at a folder named nzbget.
Your library folder should be the easiest to setup, you'll need root folders which will hold the movie folders which will hold the movie files. You can have as many root folders as your heart desires, but you'll need to manually select the right one when you're adding a movie, so keeping this to a minimum is wise. I use Movies, Kids Movies, Anime Movies and Documentary Movies and feel like this is a good number. I would not want a root folder for each letter of the alphabet. I would also not want a root folder for every genre. They would both have too many and selecting the right one when adding a movie would be a chore.
Finally, ownership and permissions of these folders. If you're using Windows, this should be easy since you'll be using one user for everything. Just make sure any services are running as your user instead of the default, which is SYSTEM. On Linux/Unix, a proper setup would be an eponymous user per daemon and a shared group with a umask of 002. It would also be acceptable and simpler to use a single user setup here with a umask of 022 or 002, but it isn't best practices. I have no idea what that will look like on MacOS, but suspect it'll be closer to the single user Windows style setup.