Your low-Dexterity character is a klutz. You'll want to demonstrate this in minor ways at first, to let your party get used to the idea.
Describe how your character is admiring apples at the fruit cart in the town market... and then drops one into the street, where it gets crushed under the wheel of a passing merchant's wheelbarrow. The fruitseller, unimpressed, tells your party, "That'll be a copper." No big deal for adventurers, sure. Do this a couple times. Maybe you accidentally knock a small animal cage open and have to catch the animal, pay for it, or prevent it from causing further market mayhem. Maybe you drop a dagger at the blacksmith's... luckily, no harm done, no fingers lost... but the blacksmith is now annoyedly huffing at your party; try haggling after that.
Then, after a couple successful adventures, offer to go potion-shopping... and see if your party will let you go alone. Say that somehow, they let you go. Roleplay being drawn to the bottle of a potion on display. Mention that you want to pick up the bottle to examine the craftsmanship of the glass, and how it refracts the light... and see how fast your companions interject with a "Don't touch that!"
Let's not talk about that one time, in the dungeon, when you were near the cauldron of boiling acid.
Or, maybe your character knows he or she is a klutz. You offer to sit in the cart instead of taking a turn clearing the trail ahead. You stand back when it comes to the heavy lifting. "Oh, it's best for all involved if I don't," you say, when the fighter wants you to open the door so they can charge in, or to the rogue who wants you to hold onto something so they can disarm the trap. You get a reputation for being lazy or too fussy, but really you know what'll happen if you lend a hand...
Did your character grow up rich? Maybe you are fussy. Maybe you've had others to do the manual labor for you all your life. You'd rather your party members do things for you, too, because old habits are hard to break, but you realize that it's not their job. But you're becoming really good at making excuses and being really polite, finding new ways to phrase your requests every time it comes up. Your party is going to catch on eventually, so expect to soon be on your own with these things, and like it.
Maybe your character overcompensates. At festivals, you makes a beeline to knife-throwing games because all you need is a little more practice, obviously. You never win anything, of course, unless you get terribly lucky. Then you let everybody know of your exceptional deed! This inflated self-recognition happens in combat, too. You roll a natural 20 (or whatever the equivalent is in the system you're playing) and suddenly your character is commenting on what a great strike that was, did you see that? You keep going on about it for a round or two, until your party reminds you that you're still in combat and can it wait, maybe, until everyone is out of danger? Okay? Please?
It's already been pointed out that your question is perhaps a little too broad. So you may want to edit and narrow it down.
However, I'll focus my answer on a specific paragraph which seems to be your biggest concern:
I am the primary tank of the team so I need my AC high. In the adventures however, there seems to be so many opponents I soak up (usually 3 at a time engaging) that I am almost in low health before we win.
Tanking is not purely about AC. And if you obsess about this single aspect it will hamper your effectiveness.
An important aspect of tanking is control.
- When fighting unintelligent creatures, it may be easy enough to put yourself front and centre and they'll attack you. But more intelligent opponents may choose to ignore you and attack "better" targets instead. Champions tend to be focused more on raw power, so you'll have to rely on your teammates to cover this.
- But you might want to consider the Protection fighting style, which defends nearby allies by imposing disadvantage on an enemies attack roll.
- Sentinel is a good choice of feat.
- Mobile can be a useful feat making it safer to move around during combat.
AC suffers diminishing returns
Basically + 1 AC reduces average damage per attack by less for each point gained. The reasons are:
- Natural 20 is a guaranteed hit (+1 AC may in extreme cases may have zero effect of the range of rolls that succeed or miss).
- The critical effect boosts damage of a high roll (so AC increases reduce average damage / attack by less for each point).
Something that can be far more effective is imposing disadvantage or removing advantage.
At the extreme end, if an enemy needs to roll 20 to hit: +1 AC has zero effect on the odds of doing damage. But disadvantage reduces the odds from 1 in 20 to 1 in 400. And removing advantage reduces the odds from just under 1 in 10 to 1 in 20.
The benefit of AC is that it's passive. It's "always on" and available to avoid damage. It doesn't get "used up" and doesn't consume actions.
However, something seriously worth considering in place of a small AC boost is the Lucky feat.
AC doesn't help at all in some situations
Many magic attacks don't require an attack roll, meaning AC is useless. So you may want to consider alternative forms of damage avoidance.
- Shield Master is an excellent choice.
- Again the Lucky feat is noteworthy.
(Though I'm a little skeptical of the benefits of the Resilient feat.)
That said, unless you're in a very heavily combat and tactics focused group, you shouldn't need to min/max your abilities. In combat, teamwork and cooperation are far more important. And there's plenty that goes on in the game outside of combat.
Best Answer
As the stats describe
From PHB Chapter 7:
Your character has the musculature of a bodybuilder, the reflexes of a cat but the cardio-vascular system of a terminal heart patient. You can exert raw power and dance beautifully ... just not for very long.
Indeed, perhaps you have an adult congenital heart defect, or stable angina or a respiratory disease like tuberculosis or asthma (not subject to magical cure for whatever reason).