I didn't find an easy way of extracting the data that I needed for the interface from the game. It's not like there is a nice software interface like some flightsims have and apparently Mechwarrior 4 is a nightmare to mod. The crew that made the MekPaks seem to have had access to some tools that are not publically available. So I bit the bullet and used Cheatengine to find the memory addresses where the game's variables are stored. It took weeks. Parameters like "Speed" or "Engine heat" were relatively easy to find but other stuff was a nightmare. I extracted dozens of parameters and some are still missing.
I have no idea how to get the firing groups and the radar content due to the way Cheatengine works. Especially the latter is really sad since it is such an important UI element. So if anyone has an idea, please hit me up. I'm continuing with the build anyway.
With all the memory addresses available, I was able to write an OpenFrameworks sketch that accesses them and displays their content on a custom graphic interface.