Anyway to tell how many people are on my server?

I'm rank 80 out of ??? so I don't know if I am near the 10% needed to climb to rank 4, so don't know if I need to grind more PvP or not before the deadline, is there a way to check that? Or a way to see how many people are on the server?

No there isn't, you basically play it by ear. If you don't get it this week, try again next but 80 seems reasonable for top 10%.

You can't know how many people are on your server, however 80th is SURELY in the top 10%