So I have my character with whom I have tons of fun rolling it. 
Here is where i think I might have broken it. 

My multiclassing was fighter, archetype brute with a barbarian with storm herald archetype.

• DPR is high as f*ck with a greatsword +1
• I took the tough feat so life is pretty dope too. 
• Blade Master Feat to improve AC too. 
• Barbarian Rage halves damage 
• Sea Storm Herald for thunder damage at the end of the turn. 
• d6 for saving throws to avoid most hits, and avoiding pretty fast death rolls with the "synthetic nat 20"

I am thinking of getting a mount soon, I was thinking on these:

1. Couatl
2. Nightmare
3. Giant Raven
4. Steel Predator
5. Retriever

If you know of any feats that could help me out, please comment below.

Don't forget to comment, is it that broken, or is it simply a good char, or does it completely suck?

For feats, definitely Great Weapon Master.  If you're not too attached to your greatsword, consider getting a glaive or halberd and Polearm Master; rules as written, you would get your modifier damage to the bonus attack from PAM and most likely your brute force damage as well.  Frankly, I would get both so that you always have some option to make a melee weapon attack as a bonus action.

I think you broke it by using UA feats and subclasses.

Quote from DxJxC >>

I think you broke it by using UA feats and subclasses.

 Yeah that plus I am not too sure what is broken here?

DPR is ok but middle of the road. 
Dex Fighter with Crossbow Expert/Sharpshooter will definitely be outpacing this in DPR and has high DEX for skill checks. 

Hexblade Paladin will definitely be outpacing this in damage, has access to heavy armor, AND has +CHA to saves. 

Barbs are VERY good tanks and can take a lot of punishment before they go down but this is in no way "broken"