Take two on shields. I read all your ideas and I decided to drop the original idea of bonus HP completly. Instead, shields provide simpler benefits as proposed in this thread.
The Shields
Code:
Name Cost Weight AC Parry Abilities
Bucklers
Metal 2 gp 4 lb. +0 +1d4 free hand
Adamantine laced 30 gp 5 lb. +0 +1d6 free hand
Obdurium laced 100 gp 5 lb. +0 +1d8 free hand
Shields
Wood 1 gp 5 lb. +1 +1d3
Reinforced wood 5 gp 7 lb. +1 +1d4
Metal 10 gp 10 lb. +1 +1d6
Adamantine laced 300 gp 15 lb. +1 +1d8
Obdurium laced 1000 gp 15 lb. +1 +1d10
Large shields
Reinforced wood 15 gp 15 lb. +2 +1d6 cover, unwieldly
Metal 20 gp 20 lb. +2 +1d8 cover, unwieldly
Adamantine laced 400 gp 30 lb. +2 +1d10 cover, unwieldly
Obdurium laced 1200 gp 30 lb. +2 +1d12 cover, unwieldly
Parry - If you have fighter's Parry ability, you add this number to damage parried when you use it.
If you don't have the Parry ability but you're proficient with the shield you're using, you now can use Parry ability as if you were a fighter, but the parry dice you get from the shield is lowered by one step (from 1d4 to 1d3, from 1d12 to 1d10, etc.)
Free Hand - Bucklers are strapped onto your arm and therefore leave your hand free to hold a weapon in combat. A buckler can be strapped only onto a medium or heavy armor.
Cover - Large shields essentially provide cover. The +2 AC they grant is not cumulative with the benefits of having cover, but other benefits of cover apply (like +2 bonus to Dexterity saving throws).
Unwieldly - Carrying around a large shield anywhere outside battlefield is not a good idea. With large shield in your hand, your speed other than walk speed is zero (unless it's granted by magic, such as fly speed - then it's unaffected). Your walk speed is reduced by 5 ft. You also get disadvantage on Stealth checks.