Ok, to differentiate(sp) servers. Its all a personal taste, "to me anyway". All servers are not the same, some run mods and some just play stock. You'll have to get a flavor of what you want. The All Seeing Eye allows you to filter out what you want and do not want, Also if you find a server you like, you can then put it into a favorites folder.
As far as "slots" or "player count go's". some games depending on what the server holds will go up to 64 slots i belive. Ping is somthing you will want to notice first. higher the ping "for me" 100 or above i tend to stay away from.
And yes, clans/squads will at least the well-known ones will require that you have some exp to back yourself up. As they tend to do competitions, or "ladders".
Have a look at one of the ladder leagues.
OGL
Edit: Clans/Squads will require your time and dedication. Just a heads-up