Don't pretend you're a rogue, because Ardents don't look good in leather. You require some real (and exotic) metals between you and the enemy. The thicker, the better. Ask for some mirrored or hydra layered plate platemail +5, as it's in a similar theme to your original gambit armor.
Item materials are also important and scale by half-tier1, but your main problem is that you're in leather armor with a dex of 16... in epic. The choice between heavy and light armor becomes critical.
Ardents use heavy armours because they, typically, don't invest in being fast or thinky. Furthermore, alternative materials don't cost more, only the enchantment matters.
The calculation should be 10 + half-level + material&type + enchantment + feats + ability score if light armor.
Displacer armor is for cloth leather or hide. Looking at the Ardent Handbook, you should be in heavy armor, not light armor.
Given that you're using leather, you should be using Anathema Leather or equivalent (adventurer's vault) to give you an extra +3. However, you're an ardent. No ardent should be focusing on int or dex, and ardents don't get off-stat bonuses to light armor.
Displacer Anathema Leather Armor brings your AC to 10+24/2+5+3+3 = 33.
Assuming you stay in chain, taking the boring Veteran's chain, in the +5 version, we get a
Veteran's Weavemail Armor +5 +5 enchantment, +10 from the weavemail. or +15 from the armor. 10+24/2+5+10 = 37, which for a shieldless leader designed to be in the second rank... is not horrible.
Assuming you invest a few of your feats into AC (which is only reasonable, considering that you're in melee with a con focus), You'll be in nagascale scale armor (+11 armor bonus) for a 38. And since you've got a 15 strength, you should have jumped into plate into epic, and +5 layered plate (+12 from armor). Add in armor specialization from paragon for a +1, and you've got a neat 40 AC.
Enemies, at level 24, should have around a +28 to hit. They will have approximately a 38 AC.
Additionally, you need to give enemies a strong incentive not to attack you or be next to you. You should have, as your at-wills, Unsteadying Rebuke and Violent Upsurge. Make it clear to the first enemy who attacks you that a) they'll get slid to the bad place on their turn, and b) they'll have all sorts of bad bad vulnerabilities. While it doesn't make up for your barely-there leather, it at least acts as a very vocal discouragement to attacking you. Which, when combined with demoralizing strike means that enemies will think twice before getting near the scary scary scary person. (Or, y'know, try to focus fire you down and kill you.) An AoE of "Here, have -6 to defenses" combined with an immediate reaction slide will inspire great fear in the DM.
1According to Andras, Heroes of the Fallen Lands, page 325, has eliminated that requirement entirely, and just automatically scales armor by tier. Take this as another reason to be using the character builder to generate your character sheet.
I couldn't quite follow your logic, but this is how barkskin works.
- If your AC is less than 16, it is now 16.
- If your AC is greater than 16 it is not changed.
- If your AC was less than 16 before you cast barkskin, so it is currently 16, and then something changes to improve your AC further, then you calculate your AC with the new item ignoring barkskin. If the new AC is still less than 16, it's now 16. If the new AC is greater than 16, barkskin has no effect and you can stop concentrating on it.
- If your AC was higher or equal to 16 before casting barkskin, but then something happens which causes your AC to go below 16 while the spell is still active, your AC is 16.
What this means is that other factors are more relevant than the thickness of your skin, once you go above an AC of 16. To explain further, your skin is your "last line of defense". If you have a shield and armor, and those combined do not yet equal 16, then an attack that gets past your shield and armor gets to your skin, which because of the spell is a 16. However, your skin does not increase your effectiveness in using your shield and armor, so if your AC before the spell is greater than 16, your skin offers no extra protection beyond this. Since AC is an abstract concept which involves your many different ways of defending yourself, that which protects you best is the defining characteristic of your AC.
Being that this is a second level spell only available to Druids and Rangers and Nature Domain Clerics, the odds of having a dex of 20 to get a +5 to your dex modifier is very low, for at least another 5 levels. (This spell only becomes available at 3rd level)
Best Answer
Armor refers to a set of armor
Armor is always referred to in sets. Taking the general description of Heavy Armor from the PHB (pg. 145):
Also Plate armor specifically, as an example, from the PHB (pg. 145):
Finally, from PHB (pg. 146), the section on Getting Into and Out of Armor says this for donning armor:
From this, it appears to me as though armor is supposed to be worn as a suit, and wearing a single gauntlet wouldn't affect your AC at all.
Therefore, no, wearing a gauntlet won't end the Mage Armor spell or interfere with Unarmored Defense or anything like that, since it doesn't affect your AC.
As an aside, some playable races (such as Lizardfolk from Volo's Guide to Monsters) have "natural armor", and according to this answer to a question about natural armor and Unarmored Defense, natural armor isn't compatible with Unarmored Defense, Mage Armor, etc. as it calculates AC differently.