I don't really like Valefor, to be honest. There's just too many people who take the game WAY too seriously, which sucks the fun out of it. I suppose if you don't mind playing FFXI for 8 or 9 hours a day, you might enjoy being on the server, but working one job a day is enough for me, thanks. Tons of drama and people holding strange grudges against each other, too.
As for population, it's gone down a bit in recent months, although that seems like the norm on most servers. On weekday evenings, it's probably 1100 or so, on weekends 1800-2000.
Like Lilbusta said, you won't have trouble finding a linkshell, the tough part is dealing with the middle school drama once you're in.