I now have a record fourteen followers here. More than the Doctor has lives. (For as long as that rule stays anyway.)
Which makes me think about group size...
Classic Doctor Who has two people in the TARDIS, which is doable and which I've done at times, but it does mean if one player misses a session it's a wash. It can work for mystery games very well as it gives you someone to bounce ideas off, and splitting up means you're both totally alone. It's also easy in rules terms - one gets the alien superpowers and one gets the narrative control of Story Points.
It's also possible to play with just one player, but the dynamic is very different - what you've got to run can go really fast when there's nobody else to distract you.
Three or four is common enough and still feels Who-ish (the show started with four, after all).
More than that, and we get to see, or need to see, a wide variety of characters. It's easier to have one crazy-powerful being like the Doctor than half a dozen, and one not-so-powerful-but-narratively-significant companion-type. If there's a lot of superpowers or Story Points around the table, the game will change. Six people are less inclined to run from a monster than two, even if you have six players who individually would be happy enough running and don't get one who'd rather get out there and twat it.
It also lessens spotlight time, although you can endeavour to give everybody a focus episode.
A classic 'party' structure can be fun, but it can feel un-Who-y having enough people to man the TARDIS properly.