Well I’m going to assume you know that the ultimate goal of the battle is to get a hammer and anvil going.
So I’ll just address your three problems.
If you’re infantry is breaking to fast that means either the enemy has higher level Infantry or your infantry has no shields or armor and is getting shot with arrows.
Make sure you infantry has good leadership and defenses against arrows and they will hold longer. Also don’t let enemy Cav anywhere near your infantry or they will get more butt fucked than Aniki.
Spears are NOT interceptor units. They are more like a deterrent. Think of them as a porcupine.
Cav vs. Cav is basically mutually assured destruction. The idea is to bait the enemy Cav into the units you have that can damage them. I’ve beat a lot of players by baiting them with light Cav, making them think there’s an easy target for their heavy Cav, only to bog them down with arrows and spears.
Another thing you can do with fast cav is to dart past any heavy cav or Spears and go for the back lines with max speed.
As for your army in the screen caps.
Spears should not be in front. Swordsmen are the melee brawlers and do better at the front. Spears are a deterrent and should be kept in the back lines and on the sides. The Romans kept their spears in the back and so should you. Cav placement is fine. Archers are fine. I never played Attila so I don’t know the meta on which unit stats are what.
Just neutralize the enemy cav then pound the enemy infantry from behind with your cav and you win.
Warhammer is such a nightmare with flying units and magik.