Back-end I would pick something super popular where solutions are well known and developers are a commodity. I would pick Java and whatever the best of the REST APIs is. Use that with some of the most popular database ORM tech, etc. It's easy to find people and you can find those who know how to make it fast.

For the front-end I'd pick AngularJS personally. I used Backbone.js for a couple of years so I know what that world is like. Ember.js might be a good choice as well but it seems like AngularJS is going to swamp it due to popularity.

I wouldn't generate any pages in the back-end at all (the exception being a couple of one-off servlets if I have binary files or other things to download which are more easily generated in the back-end). All pages would be static HTML, CSS, and JavaScript and rendering would all happen on the front-end.

It's easy to work on, it's easy to figure out where bugs are (just look at the JSON flowing back and forth), and if you focus 100% of your security on that API and making sure that you never send anything you shouldn't to the front-end and that you validate everything the front-end sends to the back to the n-th degree, you'll never have security woes.