You can't hold a buyer's feedback "hostage" on eBay like you can on other sites, because you can't leave him a negative or a negative-sounding positive, period.
So, you can either leave him no feedback or an actual positive (it can be something like, "Thank you for shopping with us" which is all I ever leave, I think the feedback that goes "Best buyer ever! OMG! I want to have his e-Babies!!!" is stupid anyway.)
In the future, tell the buyer what it's actually going to cost in postage. Nebulous questions, "Do you combine shipping?" aren't helped by nebulous answers, "Sure!" I ask what items they're looking at, and I give them a total shipping cost before they bid. It takes a few extra minutes but avoids this very problem.
Re his potential 8 negatives, depending on what he says, they may be eligible for removal. The deed is done for now, you'll have to wait and see.
Edited to add: By the way, when I get warning that a buyer is overly needy and/or unreasonable, I generally add them to my blocked bidder list. It sounds like the warning signs on this guy may have been there with his many questions, so another thing to consider for future. If your spidey senses are tingling and telling you someone's trouble, listen to them.