Where can i get decent team to get used to team games/ruleset in wars?
I doubt many clans would like to be used as a “stepping stone” but if you post in the recruitment section im sure theres some div2/3 clans that would take you on and work with you

Common mods/rulesets used so i can practise in public servers
Only real rule sets are 6v6 class limit 1 for demo and medic. And the main maps that are played are all cp(capture the point) except ctf_turbine.

Anything else to improve my skill in TF2 as i want become a better player
Competative maps and game mode used?
Which class you looking at playing? For soldier etc theres mods/games you can play such as 1v1 soldier arena, basketball and airshot maps.

Can i enter UKESA with a team even though i’m competing in COD4?
Even though that makes you a dirty dirty boy, yep i think so.