Player wants to come back as a ghost. I am all for it. But I want to make sure he is not abusing the power until the party is able to get him rezed. Here are the abilities that I am leaning towards letting him have from the Ghost monster.

Ethereal Sight. The ghost can see 60 feet into the Ethereal Plane when it is on the Material Plane, and vice versa.
Incorporeal Movement. The ghost can move through other creatures and objects as if they were difficult terrain. It takes 5 (1d10) force damage if it ends its turn inside an object.

Possession (Recharge 6). One humanoid that the ghost can see within 5 feet of it must succeed on a DC 13 Charisma saving throw or be possessed by the ghost; the ghost then disappears, and the target is incapacitated and loses control of its body. The ghost now controls the body but doesn't deprive the target of awareness. The ghost can't be targeted by any attack, spell, or other effect, except ones that turn undead, and it retains its alignment, Intelligence, Wisdom, Charisma, and immunity to being charmed and frightened. It otherwise uses the possessed target's statistics, but doesn't gain access to the target's knowledge, class features, or proficiencies.

The possession lasts until the body drops to 0 hit points, the ghost ends it as a bonus action, or the ghost is turned or forced out by an effect like the dispel evil and good spell. When the possession ends, the ghost reappears in an unoccupied space within 5 feet of the body. The target is immune to this ghost's Possession for 24 hours after succeeding on the saving throw or after the possession ends.

If he ends up being a ghost for longer then intended he will be able to unlock more ability's from the ghost monster. Such as attack and so on. We are starting off with no one being able to see him (Debating about letting the cleric see him).

Please give me your thoughts on this and let me know what you think.

Have you looked at this yet? 

I gave him this option as well. He liked ghost better. Both fit well considering we are playing Curse of Strahd. 

I think you're right to worry about him abusing the power. I might say possession might be a little op. If you're giving him possession I'd make his slam attack a flat d6. No modifier. Possession seems REALLY strong. If he winds up being a ghost longer than expected, you can give him some extra powers, but I'd say you also want his mind to slip. Make it harder for him to differentiate between friend and foe. You can slowly make him OP, but it's going to come at a cost. It would also help light a fire under everyone's butt to get him rezzed. It'd also make some fun conflict.

so what I whated to make my character as a ghost like for the campaign?