Is it a good option to use the leaders and tactic cards while using the main game board?

I never tried because I don't think ships and the extra marching speed leaders and "manage troops" bring into the game work together.

Our group always plays with leaders and tactics on the main game board. We love it!

Absolutely. SInce I own SoS our group never went back to CoK or the Main game.

Our setup always is: Leaders, Tactics, Fortresses, One time Orders (except the house special orders), ports, siege machines, SoS house cards.

Everything tuned on. Makes it a litte more difficult. "Manage troops" is not a real problem more a tactical expansion to be dealt with. In relation to the other tactics that may have been played in a turn it could be a major weakness, may it be missed power tokens, ATT or DEF Power along with stretching your armies over whole Westeros.

Did anyone try playing with Allies on the "big" board? Came just into my mind. Could be a hit. Allies plus Support Allies Tactics card could maybe balance the game to even more diplomacy. Maybe we'll give it a try.