1)
Magic items are spread out in a way you can't get them all at once, it depends on your path to victory.
For balance reasons the Banner of Wrath and the Horn of Urgoth are removed but the others are carried by individuals.
I didn't count the number of magic items but you can get plenty over time.
2)
Every mission you do counts as time spend to "get something done" before your "actual mission".
From my view of the game this was intented at some point but cut for reasons.
The result was a very linear campaign where you, except for Bretonnia, can get everything.
Thats no longer the case and you need to pick a path.
As you spend time the story doesn't wait for you anymore.
My advice for you is to not do the full campaign at once.
Instead do each chapter a few times differently to see which items and units you can get.
When you build you army chapter by chapter things start to look differently.
Also listen to the dialogues, they give advice here and there if you are running late again

Im glad you enjoy the challenge!