This is the design I decided to go with. It's not quite neat but also not completely random. It'll go nicely with the rest of the room.
I sculpted the stones in Zbrush. There are only four of them, but since the block has 4 long sides, it gives me 16 variations.
Surprisingly Youtube has loads of videos with just fire burning. It's used to create Christmas atmosphere or for relaxation. Now that's just sad.
Anyway it was good because all I need to do was take 8 screenshots, crop them and edit a little bit. Et voilá!
I've never done fire in Cryengie so it took me some time. I still need to fiddle with it. It's too stretched upwards and too thin. There are so many options, I would waste hours to figure everything out.