Solution for building an offline “composite” Eclipse update site with categories

Question

This is going to be a pretty long question, so bear with me. I'm looking for a solution to build custom update sites (or p2 repositories) for use in an offline development environment, with the following things in mind:

• Each site will contain a mix of 3rd-party and custom Eclipse plugins.

• I'd like to create a single site per IDE configuration. e.g. Developers using Helios only need to add 1 update site containing m2e, Subversive, and CustomPluginA. Developers using Flash Builder can add a different site containing m2e and CustomPluginB.

• Since development is offline, we currently mirror 3rd-party update sites with a script. The custom sites need to draw plugins from these copies.

• Our custom Eclipse plugins are currently built with Maven + Tycho on Jenkins. If possible, I'd like to configure the update sites to build automatically with Jenkins as well. Then, if a custom plugin is updated, it can trigger the necessary update site builds.

• Custom categories in the update sites would be nice.

I'm trying to find the best and cleanest way to approach this. How can I set something like this up using Tycho to build the sites? Is Tycho even the best option? Do I want the 3rd-party plugins to be copied to each site, or do I want to create p2 composite repositories which point to each of the mirrored 3rd-party sites. Is it possible to create custom categories with a p2 composite repository?

And finally, what is the easiest way to actually define which plugins and features are included in a site? In Eclipse I can create an Update Site Project which makes editing very easy, but I can only include plugins which exist in that Eclipse installation. Creating a site.xml or p2 ant script by hand solves this problem, but determining installable unit IDs and versions by hand is difficult and error-prone.

Thanks for taking the time to read all this. If anyone can actually address all of my concerns that would be amazing and I'd probably have to add a bounty to this question.