The differences between early and late game are listed here. In the end game there is no using lower tiered troops to take losses infantry bare that burden and protect your backline. The latest stages of the game are fought like crown in generally all situations.
Your marches will depend on your spec but for mage spec you are looking at:
- 30-40% infantry
- 60-70% mage
- 1 of each troop type
- No angel
- Always include beasts
Tier 10 archers have a great bonus against infantry and so are very useful. I usually include 40000 archers in the army with my mage.