I'm finally finished, and submitted my work.
This is all I was able to create with TG2Free. Displacement, and displacement. 2 days of render with masterQuality of 0.95, and AA 3, with 96 atmosphere samples (soft shadows and ray-traced atmosphere, with cloud quality of 1).
I hope one day I'll animate this scene, I like it, although I worked on it for months
On the 3rd and 4th image there is that wall-flip (camera turns upside down and back while elevating in the cave).
Thanks for all the advices and encouragement. It was a great experience.
(there are 104 quick renders in my project folder, 14 tgd and 8 tgc files, new personal record)