Travis, there is a reasonable size of neo-Nazis in the western region of the country. Jews are in ultra defense mod right now. Many Jews are thinking it best to pack up and leave. Poland is even leery about the rising tide of nationalism in some parts of Ukraine. Saying that "few" protestors are neo-Nazis is an understatement, and saying "all" protestors are neo-Nazis is an overstatement. It's more than likely somewhere in the middle.
As for your concerns about 150,000 Russians, there's nothing more than mere saber rattling going on. I think Russia is just being plain stupid right now though. The intimidation tactics are only solidifying Western Ukraine's vehement opposition to Russia. I don't know why Russia hurt itself by prematurely forcing Ukraine to sign a deal, nor do I understand why their moving around a bunch of troops to intimidate Ukraine. If I was a level headed Russia I wouldn't be too happy about the stupidity of the government.
With that being said, I suspect that Russia will allow the eastern provinces of Ukraine to revolt on their own and simply position troops in the rebel conquered territories. Russia though, I am sure, is aware of how the rest of it's customs union allies are watching it. Russia isn't going to try too much.