I think everyone else has already answered your questions, but the general rules are:
1) You have to wait 4 days from when you open the case to close it. Once closed (if closed without buyer response/payment), the buyer gets an unpaid item strike and you get your fees credited to your account. eBay will tell you when you can close a case if you visit your seller dashboard/account area. Alternately, you can opt to allow eBay to automatically close the case for you when it's time.
2) You cannot leave negative feedback for the buyer -- and he/she cannot leave it for you once the case is opened.
What I normally do with deadbeats (and I've heard it all by now, I
swear), is once I close the unpaid item case, I add them to my blocked bidders list. Unfortunately for us sellers, there's no way to warn other sellers, but the good news is that they can't retaliate against you for the unpaid item strike, at least .... and you get your fees back.
eBay's policies are constantly being revised (sometimes good, sometimes bad -- depends on how you look at it), but I'll say this at least: for awhile, the system was being skewed towards the buyer and rather heavily. Lately, they've made a lot of positive changes, I think, that help sellers with hostile/deadbeat/royal-pain-in-the-rear buyers. Of course, if you throw in all the new rules for sellers to get/maintain powerseller/top-rated status with fee discounts, it adds up to one major pain in the @$$, but that's neither here nor there, I suppose. Somehow I've managed to hang onto my reputation & account status on eBay despite all the changes, so it is more than definitely possible to do it.
Good luck, but it sounds like you're all but finished with this jerkweed anyways

!