Smite Questions

[Edgerunner]

I know you can choose when it hits.

Do you get to add the +10 from GWM to Smite?

Are you able to put Smite on a Hit if you have Hunters Mark going, or does it negate HM? IE: if you have a Concentration spell going can you still Divine Smite?

Anything else I need to know about it that would be pertinent?

[Sicarius Victis]

Yes, you can use both Smite and GWM. Divine Smite also doesn't mess up concentration, though I believe that some of the Smite spells do.

[MeeposFire]

Remember you are not adding +10 to the smite you are adding +10 to your weapon attack damage which you then when you hit choose to add smite damage to it. This may be part of your confusion. You don't chose when it hits you choose to use it or not after you hit with the weapon attack since smite itself does not hit (the smite ability is not an attack roll the weapon attack itself is).

So essentially you can add anything that goes with weapon attacks to the attack that you add smite too assuming you hit with the attack in the first place.