There are two venues in Spain, a couple more in the UK, at least one in Germany. There are more. Just some that I know of off hand. The games will probably be one-offs, testing the waters for further games in each one, and an eye on larger TV audiences, merchandise marketed, and even the possibility of relocation, or expansion, way down the road.
They will also hook up for games in places like San Antonio, and other locations where there are suitable stadiums in the US for neutral games. Then there's Mexico, Canada, and the list goes on.
Rest assured, no matter how many issues we come up with that will make it difficult, the bottom line is that ownership will continuously look for a way to expand market and create a larger revenue stream for themselves.
I don't know what the viewing audience is for games broadcast to Europe, so defer to Packinatl on that one. He's got a good handle on that info.
Enjoy about 10 years of the NFL playing with this thing. It's going to be interesting. I know that one of the things that did not make the league happy was that some teams, like the Packers, refused to give up a home game for a neutral site, like London. Now they don't need to get their permission.