Factions

lukaszmajerowicz_ESO

Is there curretnly a database out there that shows information on pvp, factions population, how all faction perform?

Taleof2Cities

ZOS doesn't disclose factions population, @lukaszmajerowicz_ESO ... but there is definitely a lot of information out there on PvP gameplay.

Start with the UESP Alliance War section:

https://en.uesp.net/wiki/Online:Alliance_War