2. I'm not sure why you can't swipe it away. If you go to your call history and tap on the call entry, then the notification should go away with that too. If not, try rebooting. I can't possibly think of anything they'd be able to do to your phone.
I've used an app called Call Control in the past that works pretty well. They have a national blacklist database that will screen your calls, but it only works if the number is in their database. You can add numbers to your own blacklist in the app, but when they change numbers that also doesn't work. The google option is to make a contact with the number that you want to block, and in the contact there's an option to send the call straight to voicemail. To do this: after you've made the contact and tapped "Done", click on the three dots in the upper-right, and tap the checkbox next to "All calls to voicemail." I use this now because I noticed that Call Control wasn't doing anything for me. I have a contact named "Blocked" with dozens of #'s in it that go straight to voicemail. I believe that Call Control has an option to hangup on calls. It's been a while since I've used the app, tho.
3. Rumor has it that the next Android will be called Lava Cake. Android has never charged for their updates (I think Apple quit charging, too. Or maybe they only charged for the IPod Touches). You'll get "free" updates on your Nexus until they decide to stop. Usually that's about 18 months. We'll be the first with the updates because our Nexuses (Nexi??) have a stock version of Android. All of the other phones require their manufactures to update their bloatware before they can push the updates. Sometimes they don't even bother. I mean, you already gave them your money so why would they care, right???