Very interesting monster for your story. It's hard to make a succubus work, but if you do it right, it can be really fun!

One would think that the kiss of a Succubus/ Incubus would restore it's own hit points, otherwise why bother?

There is a great adventure Shadow on the Borderlands (a different system) that uses an Succubus as the antagonist, shouldn't be too hard to convert.

well in my campaign we did a level zero where we went though everyone's origin it did work for my genasi fighter warlock. he had him a slave gladiator to a fire genie and basically had the story of him having a succubus slowly wanting to corrupt him well he wouldn't break his rule of only killing if his life depended on. she slowly fell in love with him because she saw the way he would act in the terrible situation he was in caring for others being this light in the darkness, and at the end of his origin she would make him her warlock so that he may escape the captivity he was in. well we had some fun with that idea like if he tried to sleep or be with any other woman he would lose his spell slots until he could entertain her and she had a desire for him to become stronger so she could create and offspring together and when he was almost killed by poison was given immortality from age and sickness the only way he could fall was in battle. 

okay only question is this what if i get to whoo my succubus what would i get besides a hot girl and a posible warlock pact

Because it's 5d10+5 damage compared to 1d6+3

Throw this at the lawful good paladin. Watch as they break their oath then kill the succubus.

I feel like the draining kiss should heal or buff the succubus in some way, and maybe give it sneak damage like it had in 3.5 so it can pick off foes with its charmed ally.

I imagine as a dm you could set it up that the souls the succubus captures are 'their property' and they trade them to more powerful devils and demons to increase their own abilities.  Though the idea for them is that the draining kiss is the last act before they leave, so typically they don't need it to give them anything immediately.

Quote from rejectthemage >>

okay only question is this what if i get to whoo my succubus what would i get besides a hot girl and a posible warlock pact

 Probably a horrible fate. Succubi are completely evil beings incapable of any kind of love. If one pretends to be in a relationship with you, she's simply manipulating you, setting you up to destroy others...and ultimately yourself. D&D is not ERP, thank Ilmater.

In one of my homebrew campaigns, I forgot to check the challenge rating and made this the second opponent. My friends were at level three and barely survived, so I decided that for the sake of any level one players that wanted to do my campaign to make it a baby and reduce its stats and XP. I also learned to use this more often, it provided an awesome battle!

You should have seen the look on the player's faces when they learned that draining kiss affects maximum hit points as well.

Quote from Herald >>

One would think that the kiss of a Succubus/ Incubus would restore it's own hit points, otherwise why bother?

Quote from Antipaladinfever >>

I feel like the draining kiss should heal or buff the succubus in some way, and maybe give it sneak damage like it had in 3.5 so it can pick off foes with its charmed ally.

 
Just to address both of these comments and anyone else coming by that may be thinking the same; a succubus is not a vampire. The draining kiss is already extremely potent; reducing max hit points by such a huge amount can effectively take a player character out of the rest of the adventuring day, and it makes for an excellent departing move to make an adventuring party think twice about pursuing it.

The important thing to note about playing a succubus is that it's not really the type of creature to get into a straight-up fight. They make for excellent manipulators and spies who work more subtly, either charming an important figure and forcing them to further her plans (and making that figure appear to be the antagonist to the players) or methodically corrupting men and women in a community to claim their souls. Often, a succubus will do both, using their charms to manipulate an authority figure to whatever nefarious purposes their master has set them to, and corrupting the souls of some commonfolk on the side.

Quote from Sangheilioz >>

Quote from Herald >>

One would think that the kiss of a Succubus/ Incubus would restore it's own hit points, otherwise why bother?

 

Quote from Antipaladinfever >>

I feel like the draining kiss should heal or buff the succubus in some way, and maybe give it sneak damage like it had in 3.5 so it can pick off foes with its charmed ally.

 
Just to address both of these comments and anyone else coming by that may be thinking the same; a succubus is not a vampire. The draining kiss is already extremely potent; reducing max hit points by such a huge amount can effectively take a player character out of the rest of the adventuring day, and it makes for an excellent departing move to make an adventuring party think twice about pursuing it.

The important thing to note about playing a succubus is that it's not really the type of creature to get into a straight-up fight. They make for excellent manipulators and spies who work more subtly, either charming an important figure and forcing them to further her plans (and making that figure appear to be the antagonist to the players) or methodically corrupting men and women in a community to claim their souls. Often, a succubus will do both, using their charms to manipulate an authority figure to whatever nefarious purposes their master has set them to, and corrupting the souls of some commonfolk on the side.

 That being said a Succubus according to some DND lore was also the original source for creating greater vampires and many fiends feed on life force for sustenance so I feel regaining hp from draining kiss should be handled the same way as a vampiric drain spell. The way you balance that out is to make them immune to normal healing spells or potions similar to undead.

Has anyone come across a ruling on what, if any, weapon and other proficiencies a Succubus may have?

If you wanted one in "deep cover", shapechanged, it'd seem logical for them to have some skills...

Quote from Adeste >>

Has anyone come across a ruling on what, if any, weapon and other proficiencies a Succubus may have?

If you wanted one in "deep cover", shapechanged, it'd seem logical for them to have some skills...

 Check the introduction to the Monster Manual, specifically the Equipment section.

What would happen if I were to make a deal with a succubus? 
anything  interesting happens, if you guys have seen people do it please share your stories 

In a scenario Where the succubus uses Etherealness  can dispel magic help with this or no?

would planar ally and plane shift help as well ?

This is my nightmare as a Paladin, I hope I never run into one of these

Funny enough I've successfully seduced a succubus once.

I'm trying to build my succubi and it's so hard because she isn't just a succubus. She's originally a wood elf who was cursed by blood magic into a succubi.