There are no announced plans for referenda anywhere else. I guess most of europe is standing waiting to see how this pans out. Despite common disgruntlement with EU, it seems most countries prefer to be in it. EU is capturing a lot of bashing because of other reasons, i believe. It is used sometimes as a scapegoat by populists.
It appears EU is immensely unfavourable in greece, yet people again and again vote government to stay not only in the EU, but in the eurozone as well.
That said, I would wager there is a lot of cognitive dissonance and disillusionment at this time across both ponds of the atlantic. These are unpredictable times.
There is definitely a renewed interest in leaving the EU among certain right wing parties in mainland Europe. For example:
Dutch far right politician Geert Wilders tweeted it was time for a Dutch referendum on EU membership.
Front National leader Marine Le Pen wants a French referendum on EU membership.
Italy's Five Star Movement wants an Italian referendum...
So yeah, various populist political parties are now using it to try and get their own 'Brexit' equivalent for their countries. It's not that serious yet (since hey, these parties aren't in power in these regions), but you can bet that if a far right or populist group gets control of an EU country now, they'll try and copy what's going on in the UK.
As for how many can leave... depends more on what the countries are and how much of an economic effect they have. If France and Germany ever decide to leave, the EU is probably in trouble. If a small country/small countries leave, or one that's running at a loss at the moment (like say, Greece) does the same, then the EU can probably survive it.
