I think we were at about 9, but I'm willing to call it seven, since that's what it's supposed to be. We had roughly 10 ice demons (who were killed in the War of the Powers), and Arien was originally with the balrogs but defected. So if there were roughly 10 to start with, we should be down to 9 now. But the 2 extra could have been lost in the final retreat to Angband or something.
We've only ever named Gothmog, though. So, really, it's Gothmog + mooks. Obviously, *one* of the remaining balrogs is going to go on to become Durin's Bane. And one will die in Gondolin at the hands of the original Legolas Greenleaf. Basically, the final number of balrogs will be determined when we get to the War of Wrath and figure out how many on-screen balrog deaths we can handle. We have to account for all of them throughout the First Age. There have been suggestions of balrog involvement in particular battles/deaths, and so we'll have to make sure we have the right number in the right place, but yes, the goal is to make do with 7 throughout the First Age.
With respect to the current battle, it seems clear that Gothmog is out 'in the field' with his army, but not engaged in the fighting. The balrogs who attack Fëanor came from Angband, so it's safe to say that these are 'mook' balrogs and that Gothmog is not with them. So, 2-6 balrogs in the group that attacks Fëanor.
But. If we have 6 balrogs attack, and Fëanor is able to hold his own, this immediately makes the balrogs look weak. We really can't afford to have red shirt balrogs. The weakest, most insignificant balrog of them all should still be burn-your-face-off terrifying. Tolkien wrote different parts of the story at different times, and obviously the balrogs became more and more fearsome fire demons in later years. We certainly do not want to reduce them to Book of Lost Tales 'Fall of Gondolin' style balrogs, so I think it very important that we reduce their numbers in this fight. Fëanor, who is with a troop of Noldor, should be facing a group of 2 or at most 3 balrogs, *not* all of them. The others can be with Gothmog. In fact, this contingent could attack without Gothmog's orders (due to whatever behind-the-scenes machinations we give Sauron), and withdraw because they think Gothmog might be upset with them for acting without orders (or something).
ALL of the balrogs together fought off Ungoliant, and she was an appropriate foe for that level of fire power. To be honest, the Noldor are no match for that. If there aren't any bottomless chasms around to drop them into.... But no, in all seriousness, we want a single balrog to be seen as a serious threat for the remainder of our series. The type of foe that no single warrior, no matter how powerful, can possibly overcome. And so...Fëanor cannot be seen to defeat or drive off *any* balrogs. I don't care how awesome he is, he just can't do it. And the contingent that comes up to save him can't do it either, though the balrogs could withdraw for their own reasons when they see the elf army arrive.
It is also unlikely that *all* of the balrogs will be present at Maedhros' capture. That will be another opportunity to demonstrate that the arrival of a balrog means the devastation of an army. We will need that object lesson, I think. (Maedhros only survives because they want him alive.)
Speaking of....we will probably want to see Maedhros as a captive in Angband before he gets stapled to the cliff. I don't know if Morgoth will want to question him personally, or if Sauron will want to meet him, or what, but...we will probably want at least one evil gloating scene. And then we get to decide if Morgoth lets Maedhros see him wearing the crown with the silmarils or not (technically, that should not happen, but I can't see Morgoth talking to him without that on, either).