[Express-js] Express CMS+Scoail API

Coming from a Java background. 
Looking for a stack based on node.js with API to make a new CMS+social based web app on AWS, exposed as WS & powered with angular ?

With a layered approach : 
1. utils
2. domain objects
3. persistance with mongodb and S3
4. services
5. facades
6. api - web services
7. front end - angular 

What framework(s) to use? What is a good way to make an arbitary response into a json string?

Start with keystone and then customize? So we get some of the functionality OOTB (out of the box ). 

Or Use koa and build our own APIs?

I am writing similar type of app in node.js. Its nodeportal.

Its still under development as I work on it in my free time. 

U can find project on github.

Current version is dependent on mongodb, I am modifying it be based on loopback, so that multiple databases can be used. 

Keystone is a good call, it'is build exactly with your needs in mind. Another thing you can use, that provides many things ootb is Sails.js

Thanks Yogesh and Gregor. Going with keystone - got at least a few things working.