With Python have we acquired a vast and deep experience through many projects where we have been using it on very different contexts: from simple database management for web apps to server-side macro-shell for administrative tasks and also as standalone application framework using graphic kits like Tkinter or wxPython. We can handle without trouble all the subtle differences between Python 2 and 3, and can manage a complex threading structure with security and efficiency.
TCP/IP network in general is another of our major specialties, since we have been managing network-based applications for more than 15 years. We can deal with TCP/IP protocols at the low level (like implementing custom mechanisms to get reliable UDP transmissions) as well as apply them to specific content (like video streaming over HTTP or RTSP). Management of HTTP headers is for us an every-day task, that we have execised on many HTTP-based applications, and we can handle it efficiently. Network traffic simulation doesn't belong as for now to our portfolio, but we would be glad deeping into this interesting subject.
As for the additional tools you mention, we know PhantomJS that we have used for testing purposes, and we feel very comfortable working with it as we find it a very valuable tool. Putting all together, we think we could bring good results for you on this project, and would enjoy discussing it in detail with yourself.
Regards
The Bramfeld Team