Edit: revised with the OP's classes and stats in mind; oh, and the house rule on allowing the Animated Shield for a monk which considerably changes things.
No, Magic Vestment cannot be applied on the Bracers of Armor.
The simplest way to get a good Armor Class is to wear an Armor (and wield a Shield), and spells such as Magic Vestment build on this, restricting their improvements to Armor (or clothes) and Shield.
There are classes that allow adding your Wisdom bonus to AC (in place or on top of your Dexterity bonus), however for a full caster the synergy would be poor.
The generic way is to use:
- A good armor, a Mithral Chain Shirt costs 1,100 gp and grants +4 AC/+6 Max Dex/0 ACP, you can go one step further with a Mithral Breastplate thought it costs 4,200 gp for only +1 AC at +5 AC/+5 Max Dex/-2 ACP. I would personally opt for the Chain Shirt because 3,100gp for just +1 Armor AC (and -2 ACP to boot!) is costly.
- An Animated Heavy Shield +1 gives you a +3 Shield bonus to AC.
- Some Gloves of Dexterity +4 for 16,000 gp give you +4 to Dexterity, which translates to +2 Dexterity bonus to AC.
- You can use Magic Vestment on both Armor and Shield, remember that it adds an Enhancement bonus, and thus overwrites the existing +X and does not add to it.
With this (simple) basis, you get:
- an Armor bonus to AC of +5
- a Dexterity bonus to AC of +4 (+2 increase)
- a Shield bonus to AC of +3
For a total of +12 AC. As a 9th level Cleric, casting Magic Vestment (+2 Enhancement bonus at this level) on both Armor and Shield bumps this to +15 AC.
- 17,100 gp / +8 AC (compared to running naked) with Mithral Chain Shirt (+4) + Gloves of Dexterity +4 (+2) + Magical Vestment (+2)
- 20,200 gp / +9 AC (compared to running naked) with Mithral Breastplate (+5) + Gloves of Dexterity +4 (+2) + Magical Vestment (+2).
- 29,000 gp / +9 AC (compared to running naked) with Bracers of Armor +4 (+4) + Monk's Belt (+5)
Note: I purposely ignore the Animated Shield and its enchantments as your generous DM allows it in both cases.
While your setup is fun, it is a needlessly costly basis. Starting from the Mithral Chain Shirt gives you 11,900 gp to increase your AC.
Now that this is done, let's see the bonuses:
- You should start by getting some Natural Armor, Insight, Deflection and Dodge bonuses; see http://aaronwiki.us/index.php?title=Armor_Class_Guide for the most cost efficient ways to increase your Armor Class: it suggests that at level 12 you could be looking at +1 Dodge, +2 Deflection, +2 Natural Armor and +1 Insight (for a total of +6 AC)
- The domain Balance from Player's Guide to Faerun, p. 84 has for specific bonus the ability to, once per day, get your Wisdom bonus to AC for 1 round/Cleric level.
- The feat Expeditious Dodge from Races of the Wild, p. 150 grants +2 Dodge bonus to AC whenever you move 40 ft. or more; it also counts as Dodge for the purpose of fulfilling pre-requisites
- The feat Mobility from Player's Handbook, p. 98 grants +4 Dodge bonus to AC to avoid Attacks of Opportunity when moving (and has Dodge as a pre-requisite). Do remember that Dodge bonuses to AC stack.
- The feat Protection Devotion from Complete Champion, p. 61 grants, once per day, a +2 to +7 Sacred bonus to AC against evil to you and every ally within 30 ft for 1 minute. You can use it one extra time per day for each 3 Turn or Rebuke uses that you expend.
- The spell Barkskin from Player's Handbook, p. 203 grants +1 Enhancement bonus to Natural Armor, and +1/3lvls (up to +5), for a total of +4 at level 9, is accessible through the Plant domain.
- The spell Sirine's Grace from Spell Compendium, p. 191 grants, among other things, a +4 Enhancement bonus to Charisma and a Deflection bonus to AC equal to your (newly adjusted) Charisma bonus for 1 round/level; it can only be cast by a Bard or Druid and has a target of Personal, however it could be used as a basis for a custom item.
Alright, let's I don't see you changing your domains and feats overnight, however:
- Amulet of Natural Armor, 2,000 gp, +1 Natural Armor bonus to AC
- Ring of Protection, 2,000 gp, +1 Deflection bonus to AC
- Ioun Stone, Dusty Rose, 5,000 gp, +1 Insight bonus to AC (very costly, not included below)
That is, for 4,000 gp, you can get +2 AC.
- 21,100 gp / +9 AC (compared to running naked) starting from Mithral Chain Shirt
- 24,200 gp / +10 AC (compared to running naked) starting from Mithral Breastplate
Those are, of course, the permanent items; you can also use temporary buffs (items, spells, potions, ...) to have a higher spike AC if it still matters.
However, let's check the total AC:
- 26 AC with Mithral Chain Shirt and the bonuses
- 27 AC with Mithral Breastplate and the bonuses (3,100 gp more expensive, and -2 ACP)
- 25 AC with Bracers of Armor (7,900 gp more expensive)
- 28 AC with Bracers of Armor and the bonuses (16,900 gp more expensive)
This seems like a good permanent AC; at this level the Armor Class guide is only at 29 AC.
With that being said, I feel the need to warn you: a character is NEVER obliged in any way to use its Attack of Opportunity on the first opportunity it has. An intelligent character, unless specifically goaded, is thus quite likely to ignore the running fool and keep its sole Attack of Opportunity for a worthy target... or one it feels it has a chance to actually affect.
I thus feel the need to mention that:
- should you optimize your character's AC without optimizing the rest of the party's AC, then your tough character runs the chance of being ignored by mundane foes (who have little chance of affecting it), which is detrimental to the goal you are attempting to achieve
- should you optimize the whole party's AC, then you will force the GM's hand into either looking for heavier hitters or switching strategies, so as to keep your party challenged; after all, with no challenge it would be boring
If your goal is to protect your party, I thus advise you to spend a bit more time selecting disabling spells; it will be more effective.