There are some comprehensive torrents that just have everything but it’ll take you ages to download it all. I managed to get the entire collection about ten years ago and just added new releases as they dropped.

Short answer: I'd probably start with TVC for video stuff and MAM for audio stuff. They definitely won't get you all the way there, but they'd be a decent enough start for a collection and ratio isn't hard on either one.

Longer answer: The main series itself and the theatrical movies shouldn't be too hard, and even the main spinoffs (K9 and Company, Torchwood, The Sarah Jane Adventures, even Class) shouldn't be too bad. I think where you're going to run into issues are things like the fan reconstructions of lost episodes, the various animated stories, short stuff like the Tardisodes, there's the behind the scenes programmes (Doctor Who Confidential, Totally Doctor Who, Doctor Who Extra, etc), the Red Nose specials, etc.

Then you get into the other stuff - official BBC stuff but not-on-video, all the fan stuff made during the lost years that had official / semi-official / unofficial-but-winked-at licensing, etc: There have been official BBC audio plays and radio dramas. I think most of Big Finish audios have leaked, though collecting and keeping up with them would be a chore - it's a pretty big collection, and they still make multiple stories every month. The ReelTime and BBV videos can probably be tracked down with a bit of effort (I do like the Myth Makers series). I don't know if any of the theatrical productions have been professionally filmed, though there's likely amateur video (but watching an audience video is often tedious and I'm not sure how much you want to get into this). Etc, etc.

If you want to get even further into things, there are novels and comics and annuals and all sorts of other stuff. I guess the question is, where do you want to start, and how far do you want to go?

Again, personally, I would start with TVC and MAM and see how far I wanted to go. I mean, the show has changed a lot over the years, some of it's missing, it's in various formats, stuff in different formats us considered canonical or non-canonical depending on the person. Even if you're willing to sit through black-and-white video recordings from the William Hartnell years, do you want to sit through fan reconstructions of ten of the twelve episodes of "The Daleks' Master Plan"? Do you want to read Lungbarrow in preparation for the TV movie? It's a long, complex, and time-consuming continuity.

Have you looked into a Plex Share? Low cost and access to pretty much everything. PM me if you want more info on one.

i went to 1337x.to, searched "doctor who" and sorted by size. the largest torrent claims to be the complete classic 26 seasons 1963 - 1989 (I assume you know this but based on your question you might not, do not be torrenting unless you have a VPN turned on)

Probably Usenet.
High retention piracy.
Or you become a member of a private tracker and maybe they have a super collection.

Usenet is pretty much the only place where you can find truly everything. Many of the original seasons and episodes are lost media. So you can't actually get everything without a private tracker or Usenet

@giancarlozero@mastodon.social

FYI - UK BBC iPlayer has everything on it now. From the first doctor to all spin offs.

I just saw this article on the subject

Everything doesn't exist. There are 97 episodes currently missing. I started watching from the first ep a while back, there was a fair few more missing at the time, but I pretty soon got lost with big chunks missing.

You can use iplayer through a VPN if that's useful to you.

Bit of a tangent, but it's the 60th Anniversary of Doctor Who, so BBC Sounds has loads of the audioplays available to listen. Those should be available to listen, even in Australia. They invariably star the original actors, I just listened to one which stars David Tennant and Tom Baker.

Can u share with me when u get them