First time seller, expensive item, I would estimate >75% of this being a scam.

There is more then one possible scam here:

(1) You give him your paypal account info, so he can send you the money. He sends you a spoofed paypal email making it looks like he paid you, and hopes that you send it without actually checking paypal.

(2) Same as above, except the spoofed email includes a link to sign into paypal. That link is bogus, and they rob your paypal account.

(3) Hackers already has control of a compromised paypal account. However, he cannot transfer the money without getting caught. He messages someone selling something that is easy for him to pawn/resell/whatever. He sends the money, and you send the item. He uses an address that is not his, but he has access to so that he can intercept the packages. Paypal catches the comprismed account after the payment occurs, and takes the money back from you to give it to the actual owner. Scammer then sells the item elsewhere. You are SOL, without seller protection.

(4) Same as above, except the scammer just fakes that his account was compromised. He gets his money back.

Even if this isn't a scam, it is against ebay policy. If someone wrong happened in the sale and ebay looked through the messages you would get banned for selling off of ebay. His feedback doesn't mean anything, as the account could be compromised. Even if it wasn't no one he is scamming can leave feedback or complain to ebay without risk of getting banned.

Tell him that you would be happy to sell him the item, but as per ebay policy you must complete the transaction through ebay. Lower the price on the buy it now to whatever he suggested, or use the make an offer feature if he if available. No matter what, only ship to the address that is given to you by ebay when he completes the transaction. Ignore any email you get, only pay attention to the messages on ebay and paypal directly. Use signature required when you ship it.