Help me chose a stack for real time dashboard app

I will build a dashboard system for my apps, where a page will have several widgets that draw charts, tables and glyphs representing potentially unrelated data.

The client will be HTML5 and I can push for only modern web browser. Not worry for legacy stuff.

My big problem is what stack use for this. I want to store "tables" for use in the charts and in real-time update the widgets.

For example, a invoicing widget will show how much $$ have been collected today. In the "table" will have a row for each total of the invoice:

  inv = 1; total = 50

  Total: 50

and the widget will draw that. When new data is pushed:

  inv = 2; total = 100

  Total: 150

The widget will show in realtime the total to the end-user. The data will be collected by agents made in python/ios.

The data is private for the user company, so is important the security/privacy - that is what make me distrust client-only tech like firebase, pusher-. Eventually I will need to purge too old data (ie: I only need to keep as much data is necessary to proper evaluation of the info need for the end-user. For example, only keep 1 month of invoicing totals).

My idea is to have data feeds and display widgets. Several widgets could display info on a single data feeds. I need to attach alarms to react to this data, ie, if the invoices of today are 0 then send a email or something like.

I wonder which backend/platform will bring me closer to the build of this system. I have experience with python/django/.net/postgress but could accept the use of something else if solve best this kind of app behavior, I'm not afraid to learn new things. I deploy to heroku, but could accept a change.

So far, I have a look a firebase, redis, derbyjs, socket.io, node.js, 0mq, brubeckt, angular.js, batman.js, meteor (look like the real-time thing is exploding now, and every second something new happend, making me very difficult to see what to do)

Is not like with a classical CRUD website where is easy to see how fit something like django as a tool to make that website.

So, my problem is that I don't see a clear stack. When I meet ruby/django (despite that I have not idea about python/ruby) was very clear to me what exact kind of software could be built with them. Because this stuff is very new, I can understand that not exist a clear "winner", that is the reason I look for suggestions.