To Dontadow: Here's the Plots & Poison info. It's 3.0, and I'm keeping most of the detail for the sake of being thurough. You'll have to adjust it a bit, but it shouldn't be too hard to do.
My opinion: drop Ambidexterity (obviously), and replace Shield Specialization with Improved Shield Bash. I'd replace Ambidexterity with Improved Shield Bash as a prereq to MC I. The prereqs for MC II would still be feat intensive enough with the loss of one feat.
Martial Arts Style: Mithral Carapace I
Pre Reqs: Dex 15+, Alertness, Ambidexterity, Deflect Arrows, Double Shielding, Improved Unarmed Strike, Shield Proficiency, Shield Mastery [Any]
Benefit: A +3 competence bonus to damage with a shield bash attack
Martial Arts Style: Mithral Carapace II
Pre Reqs: Mithral Carapace I mastery (this is not a feat), Combat Reflexes, Cut Arrows, Improved Deflect Arrows, Shield Mastery (Large Shield), Shield Specialization (Large Shield), Two Weapon Fighting
Benefit: Any enhancement bonus to AC with large shields you wield count as enhancement bonuses to attack and damage when you make a shiled bash with them. This is a supernatural ability that refreshes as a free action every time you make a shield bash.
(Poster note: From the wording, I'd say that during that split second you attack, it doesn't count as both. Folks with feats that allow attacks during that time might catch you at a reduced AC).
Feats:
Double Shielding:
Prereqs: Dex 15+, Alertness, Ambidexterity, Shield Proficiency, BaB +3 or better.
Benefit: If you wield a shield with a -1 ACP or better, you may wield another shield with a -1 ACP or better with the other hand and gain the armor bonuses from both shields. You suffer the combined ACP from both shields.
You may make shield bash attacks with your primary hand without penalty, but you lose it's AC bonus until your next turn. If you employ two bucklers and use two handed weapons (including two handed ranged weapons), you incur a -2 to all attack rolls.
You may take this as a fighter bonus feat.
Shield Mastery:
Prereqs: Shield Proficiency
Benefit: Pick a shield (Buckler, small, large, tower). Whne using that type of shield, the ACP is reduced by 1. This penalty cannot be reduced below 0.
This feat may be taken multiple times. The benefits do not stack. You must chose a new shield each time you take this feat.
You may take this as a fighter bonus feat.
Cut Arrows:
Prereqs: Dex 13+, Delfelct Arrows, Imprived Unarmed Combat
Benefit: When using Deflect Arrows, you do not need a free hand. You may use your feet, weapon, or object in hand. If successful, you may deal damage to the projectile that would have hit you.
(Poster Note: Great for those who use returning weapons or recoverable projectiles).
Improved Deflect Arrows:
Prereqs: Dex 13+, Combat Reflexes, Deflect Arrows, Improved Unarmed Strike
Benefit: When using Deflect Arrows, you may deflect a number of arrows equal to your dex modifier +1.
Shield Specialization:
Prereqs: Shield Proficiency, Shield Mastery
Benefit: When you make a shield bash with a shield type you have mastered, you may regain the shields AC bonus as a free action. If you choose the buckler for this feat, you may shield bash for 1d3 damage and not suffer the -1 with off hand attacks (with weapons or shield bash). You regain the buckler's AC bonus after making an off hand attack.
If used with Double Shielding, you may regain the Ac bonuses for both shields as a single free action, provided both shields are of a type you have mastered.