TL;DR: Yes, you should be able to get all these bonuses, provided you have the attunement slots available.
In general, you are only allowed one equation to calculate your AC. These equations might be:
You might have multiple of these, but can only use one to calculate your AC. A multi-classed Barbarian, Monk, Dragon Sorc could calculate their AC any of the following ways:
10 + Dex (No Armor Bonus)
13 + Dex (Draconic Resistance)
10 + Dex + CON (Barbarian)
10 + Dex + WIS (Monk)
You can also increase your AC by getting bonuses to your AC. They might come from:
Equipping a shield (+2 AC)
Wearing a magical item (+1 ring of protection, +1 cloak of protection, etc...)
Wearing an enchanted armor (+1 Plate Mail, +2 Studded Leather Armor, etc...)
taking a feat or class feature which increases your AC (fighting style, dual wielding, etc...)
You are allowed to add as many of these as you can equip. Standard equipping rules apply: You cannot wear more than one cloak, pair of boots, etc... You gain no benefit for wearing half of something (if you wear two magical gloves with different enchantments, you get no benefits from either). You cannot equip two of the same item (you can have a ring and cloak of protection, but not two rings)
While one might say that if you remove the boots or gloves or helmet from a suit of plate mail, it's no longer good, but normally, you are allowed to swap out peripheral parts (bracers, boots, etc...)
In your case, the bracers would not count as armor (there is no similar item on the armor table in the phb), so they could be used with your draconic resistance.
The mask, however, is a bit trickier. Adding an ability modifier is more along the lines of a new formula for calculating AC (AC = 10 + DEX + CHA) rather than getting a static bonus. However, the way it is worded makes it seem like a static bonus that changes only when your CHA changes.
Given that your new AC (assuming 14 DEX and 18 CHA) with everything equipped would be:
AC = 13 + DEX + CHA + Bracers
13 + 2 + 4 + 2 = 21
I personally would be inclined to make the mask and Draconic resistance mutually exclusive (the Dragon mask is another way to calculate AC). However, RAW, I think you can wear everything. Remember that this will take up two of your three attunement slots, so you will only be able to use one other magical item that requires attunement.
That being said, your DM has the right to make either ruling.