For the first question: you can find vials doing quests that remove all the negative traits you got, there rare, but out there.

The second question is something that I am wondering myself.

Based on my 1 week of experience with the game, you can significantly reduce the damage to your champions by taking the following precautions:

1. Always allow them to recover their hit points completely between fights.
2. Equip them with the basic items of armor you'll collect in the early stages of the game - they need the protection more than your sovereign.
3. Include an expendable unit like spearmen in your army. Combat resolution seems to take out the weakest unit first and work its way up.
4. Not all champions are fighters - read their biography - some are administrators and, my experience thus far indicates if you put them in your city instead of your army, they'll make you tons of money.
5. Before getting into a fight with someone more powerful than you, or an unknown - save the game! This game really needs a quick save button on the main screen!

The Tilda Herbs used to make the restoration potion are quite common in the game - most bear dens seem to have some, but the old woman who knows the recipe for the potion is rare, I'm not sure if there is any way to get the potion other than have her make it for you. Even then it will only heal 1 champion.

Im sure there is a better way to do this but I do it by holding the shift key and selecting all units I want in my group.

Just to clarify; if you click the stack you will see (at the bottom left) which units are on that hex, after that you can select individual units by clicking on their icon. The selected unit will have a thick yellow ring around its icon. You can select more than one unit by holding shift and selecting more units.

Also, if none of the units are selected (no thick yellow rings around any unit icon) then it counts as all of them selected. So ya...  its kinda unintuitive.    

 https://forums.elementalgame.com/

BTW - Ctrl +S is quick save.

The injuries are a result of the champions being too overpowered in the first beta.   There needed to be some risk to using them as a one man army.  It is still a viable strategy but has the risk of getting them an injury.  

That said, I think there should be a high level spell that removes injuries.

I agree with that just 1 page in the options section or something like that.

Sincerely
~ Kongdej

You don't, caravans are spawned from having a trade treaty, you cannot build them.
(They appear automatically from trade treaties)

Sincerely
~ Kongdej