!. Yes there are, there are the old possessed heads you could use as well as the new ones. The Khorne Berzerker Vampire head. and a few heads where they only have the respirator on. But overall Chaos Marines see the benefit of keeping their heads covered in a war zone. After all, ascension to daemonhood is a bit hard if you have a bolt lodged in your skull.
2. If there is it would be on eBay, Battle Wagon bits and maybe on GW's online site.
3. Yes, the Chaos Rhino has spikes on it, included in a separate sprue. however if you don't put spikes on it, no one will give a crap as long as you use the CSM rules for it.