+2 Strength. As a pally, your primary job is to hit things with bits of metal, so you want to be able to do it as hard and a regularly as possible.
There's other options, such as using the Green Flame Blade and Booming Blade cantrips for your melee attacks (from Sword Coast Adventurers Guide, SCAG), so Magical Initiate can be worth a look at with your high Charisma, but as a first time player it's often easier to just go the simple route. Hit stuff, smite stuff, learn to use a few other combat options and how to protect your team members, do a bit of healing sometimes.
The other feats you mentioned are good too, but Strength is your primary stat, so boosting it all the way to 20 eventually can't hurt. More hits, with an extra attack coming soon, is good.
Rounding out Con can happen a bit later, as can Sentinel (others might have a different view on this, but as a first timer, I'm keeping it simple).
Do you have any experience with other versions of DnD? Your post count suggests at least a little.