There are 3 isolated
continuities in audioland.
(the first two happened at the same time on top of one another.)
The monthly range of big finish, where he's with Charlotte Pollard, an Edwardian Adventuress to begin with, kept going for another 10 years. (3 or 4 stories per year plus specials sometimes.)
8 did 4 years with the adorable
Sheridan Smith (30 stories) which was made by Big Finish for BBC7, which means that they were broadcast on the radio, and then sold as dvds.
Paul went on a break of sorts from the monthly releases (Tom Baker picked up his slack.) but has been releasing Large Boxsets for the last couple years called Dark Eyes which is almost the same volume as 4 monthly releases, but it's just the one ongoing epic story. Two Boxsets have been been released. They won some awards, so the next two were green lit immediately.
You might want to look at the UNIT Dominion BOX Set, because it introduces a new actor as the Master, who is a little cheeky, but that's the same Master squaring off again the 8th Doctor in the next Dark Eyes box set, and it's best to be prepared for these things.
Exactly how many thousands of dollars are you willing to spend on this curiosity?
Oh, Big Finish released a high profile 5 Doctor story (4, 5, 6,7 and 8.) last year called Light At The End which had the actor who played the Master in the Keeper of Traken as the big bad, who shows up from time to across the Big Finish Spectrum, and that got all timey whimey pretty fast.
Here's the order of almost everything big finish has made in the doctor Who range.
Daunting, but you can figure it out from there.