One last tip, your ruler can serve as an expendable hero, for doing gold wonders or stuff way above your current power level you can sacrifice your hero army and revive your hero. That will leave you vulnerable, but you won't lose your hero like when a regular one dies in battle.

In regards to your first tip, which is a great one btw that I didn't necessarily consider. But, if you split off your troops, even though they are still fighting the same battle, I'm assuming those split off troops won't benefit from the hero skills that boost the experience of units in their army.

Hero ball was fun. Used industrious for the scouts on the mountains getting gear at times. Talented collectors and fabled hunters were my other two. Thought it was fun getting a lot of gold that way and resources.

Hey thanks for the tipps! Really cool ideas in there and some general guidelines which I will be using from now on!

Maybe videos on each class like all support or battlemages

I can't see how you need one army per front. I find that frequently (past turn 50 or so), the AI invades with 6 doomstacks. 36 units in total. Sometimes city states will send out a raiding party of 6 guys, but that's a different thing.