well, let's see...these are the tube mics I have in the studio mic locker, in the order that I acquired them. But to answer the original question, I would be fine with 5.
Soundelux E47
Telefunken AK47
Manley Reference C (w Telefunken 12AT 7tube swap - tamed the high end)
Brauner Valvet
Flea 47
Flea 49
Pearlman TM250
Flea 12
I use the E47, Pearlman, and Fleas the most. The 49 and AK47 are great on acoustic guitars and the 12, 47's, and TM250 and Valvet are fantastic on vocals.
The album project I just finished saw the Flea 12 used on the male vocals for one singer, and the C414-U BLS on the other male singer. When I replaced the scratch vocal tracks, which were done on an SM7 (original model) with the final takes, we tried all the Fleas, Manley, Pearlman, Valvet, and E47, and the 12 was the one that sounded right and sat in the mix perfectly for one voice and, after none of the tube mics worked for the other voice, I set up the AKG and it was the one that worked. As usual, it just depends on the voice,
To my ears, the 12 sounds like a nice coating of sonic velvet has been added to the vocal. And BTW, it was a near-tie between the 12 and the TM250 on the baritone voice being recorded, but the 12 had the more 'finished' sound on the voice being recorded. The other voice was a high tenor, nasal sounding singer with tonal similarities to Ricky Skaggs and the 414 just brought the magic.
I should probably trim the collection one day soon, just based on regularity of use for my specific needs.
And FWIW: There are some fantastic non-tube mics that get a lot of use in my room. High honors go to the Shoeps V4U- it's just stellar, Blue Kiwi - always works, and AKG C414-B ULS - a real studio workhorse mic...it can handle anything and everything.
Plus, my old SM7, which is from the early 80's, that stays on a boom ready to go 24/7.