Paladin Build Advice

Hey! I’m a returning player to dnd and I’m pretty out of practice, plus I was already a sort of high beginner low intermediate experience player before, so I don’t recall too much about how to play and build characters yet. Got a campaign coming up and I’m rebuilding an old character in a different setting, but I don’t really know what the best way to go about it is. He’s a doctor essentially, a poison dragonborne who makes antidotes and whatnot with his knowledge and tries to help people in his very chaotic and broken city. He doesn’t have any specific God but I figure he probably will have one as a paladin, but I’m not really sure what oath to go with. I want him to be useful of course, but I don’t mind trading a thing or two to suit him flavor wise better. He’s not *just* a healer because this city is really rough, and he’s a big intimidating guy who sometimes has to fight to scrounge up herbs and medical supplies for his practice to help others, and he has to be tough to make it here, so he does need to be decently strong. 
Does anyone have advice for a good build for a dragonborne that’s still strong but thematically appropriate for someone whose job is to be a doctor in a Gotham-esc city? We’re going to start at level 6 and the dm is a fan of homebrew and alternative contents so the range is any sort of subclasses/oaths I could reasonably get access to to build him. 

Are definitely bent on a paladin?   There is a monk subclass that can be used as a doctor.

https://www.dndbeyond.com/classes/2190880-monk#WarriorofMercy

I suppose I could change the class, but I do sort of want to keep as a paladin. It’s familiar and I feel like thematically it works well with what I’d like to achieve. 

keep it a paladin.  I was not sure how tied you were.  Having come back after a long time out, I did not know about new subclasses (to me.).

5 or 5.5?

Technically, paladins in this edition no longer need to be affiliated with a god. But it’s fairly common house rule that they do, so check with your DM about that, and if they do require a god, which pantheon they’re using.

I’d look for a background that gives proficiency in herbalism kits, or find some way to get it as that will let you make antitoxins and potions of healing. As for oaths, devotion could fit, or maybe ancients.

You’ll want the Hermit background, or at least something based around it for the healer feat. It will also grant you Charisma and Constitution boosts.

With that much Charisma, you’ll either want to go with the Oath if Devotion to boost your attacks or take a one level “dip” in warlock for the Pact of the Blade Eldritch Invocation to attack with Charisma instead of Strength or Dexterity. 

Also, with high Charisma, you’ll want to go with Intimidation and Persuasion as your boosted Paladin Abilities.You’ll get medicine and religion by default for having the Hermit Background.

Beyond that, if you are going straight Paladin with no multiclassing (no dip in Warlock for example), choose between a Strength or Dexterity build. (If you multiclass, you should actually always go Strength since you have to boost it so high already). Strength uses heavy armor, and dexterity uses medium armor. You’ll have to check which weapons use what stat (if not both), but generally you want to either two weapon fight with a shortsword and a scimitar or fire long distance with a crossbow(s) but have a rapier for melee if you go dexterity. For everything else, there’s Strength.  

Your species (race in this case)  is likely an older one, which is fine as long as you own ii or play with someone who has access to it and the group is ok with using older content. If not, you may just have to go with the Dragonborn species from 5.5 and flavor it.

Oh, if you are worried about feats, most would take War Caster at level 4 to even their +2 Charisma from 17 to 18. From there, take the Ability Score Increase (ASI) both in Charisma at level 8 to max it out at 20, the Resilient (Constitution) feat at level 12 for a 17 in Constitution, both ASI in Constitution at level 16 to take your Constitution up to 19, and finally either the Boon of Combat Prowlness or Boon of Dimensional Travel to max out your Constitution at 20. That’s what I would do anyway based on the basic content, but you can try different combinations, especially if you have other source material.

in summary, you probably want a Charisma based Devotion Paladin with the Hermit background. Everything else is up to you. Good luck!