First I will say that I like tubes and think they are way cool and can sound really good.
Then I will say my approach, FBOFW, is keep tubes to a minimum because there is additional work involved to care for tube gear properly and there are many ways to get good sound without them as well.
If one will be using tubes, two ways to keep them to a minimum accordingly:
1) use in pre-amp only
2) use in amp and use fairly hi efficiency and tube friendly (higher impedance, not 4 ohm) speakers to keep # of tubes, size cost and complexity to a minimum.
Tubes wear over time and are more noise prone than SS. They also will tend to go bad completely more often.
There is something to be said for keeping things simple and relatively maintenance free. I shoot for that but I still run 6 tubes in my arc pre-amp in my main rig. It sounds really good, but my preference would be for the same quality sound with no tubes to have to deal with. Its probably possible, but so far I have been able to live with just occasional tube related noise and issues without too much pain.
OR if you are one who just loves tubes and the more the merrier no mater what, just have at it! But expect more time and issues dealing with noise and other problems when tubes are not performing up to par compared to the alternative. Tubes tend to get HOT, so chance of fire has to be higher in general I would think, though chances of happening with gear in good working order that is properly cared for is probably not too great. Its a real issue though and worth some consideration. YMMV.