The nature of Balrogs

I'm sure this topic has come up over and over again, so sorry.

We have already established that no mortal could defeat a Balrog singlehandedly ( with the definite exception of Hurin and perhaps Turin ) and very few Elves could defeat MORE than 1 Balrog with the exception of Feanor, Fingolfin e.t.c

Some here have mentioned that they read somewhere that there were only 7 Balrogs all together? This really doesn't make sense to me. I mean for 7 they get around a lot don't they.

In the wars mentioned in the Silmarilion I got the impression that there must have been at least 25 Balrogs all together.

Gandalf killed 1 before he became Gandalf the White ( although I got the impression that the Balrog in Moria was weakened after remaining dormant for so long )

Ecthelion killed Gothmog.

Feanor must have killed at least 1 ( speculating but come on! )

Glorfindel killed 1.

How about the wars with the Noldor? At least 1 must have been killed during all those skirmishes and wars?

That leaves 2 Balrogs for the War of Wrath ( I have leant the Silmarilion to a friend so I can't quote form it sorry ) and doesn't it say something like " and Morgoth issued Orks and Balrogs against the host of the Vala"

What about Morgoth's personal guard?