This level isn't hard. But there are no shield spheres, only those that you can salvage from the mechs. So I needed quite a few attempts to get one above 100.
There is no yellow key. Probably those 'secret documents' are stored behind them. (I went in using cheats, there is nothing interesting there. One smart missile, a shield spheres, energy blobs and an angry ptmc defense robot).
Probably this level is made by Parallax. Where they finally put in the introduction of the Miniboss they owed us from the First Strike.
Calmarius currently has 52,422 views spread across 150 videos for Descent. His channel published over 1 day worth of content for the game, or 33.54% of the total watchable video for Descent on Calmarius's YouTube channel.