Not GP but ionic is really solid. It helps to think of it mostly as a CSS framework with a tool chain for deployment and testing. Theres also a lot of examples and a pretty big community around angular + ionic.

Thanks. I haven't done webdev in many many years so all the new front-end & back-end frameworks are a bit overwhelming.

One thing I haven't decided yet is what to use to build the "pre-login pages". The SPA itself will be only accessible after a login page, but before login there will be a bunch of pages (Home/Blog/Help/etc..). Should I use Angular for those pages as well?

The convention is usually to serve the SPA via a CDN regardless of server side authentication and then have client-side routing prohibit users from rendering authenticated pages. This assumes data is authenticated/authorized within a server side api and no privileged information is in client-side code (it never should).

In angular this is usually achieved by watching for state/route change events and deducing whether or not a route should be redirected or allowed to progress based on the status of the currentUser.

It sounds a little hairy but in my experience there are ample resources detailing the process and realistically it's about ~30 LOC.

Cant say its "additional" but Polymer + it's material design components work great on both desktop and mobile.