Im thinking the minimum is 9 at best. 1 in tunnel one, 2 in tunnel two, 2 in tunnel three and 4 in frozen tunnel. The fungi one in the first tunnel will kill you for sure. The lost world one will kill you, and the cave trolls will kill you. The mammoth one in the ice caves might actually be possible to live through. The nether in tunnel 3 will kill you, and so will the underworld. I think you can get an angle on the hell crystal and live after getting it. Sadly, i think the first 4 in the frozen tunnel will get you killed, unless maybe the very first one doesnt but you wont get any other crystals if you live after getting it. Im pretty sure you can survive the final dark noxesium in the lava area, it would just be tough. Everything else would just have to be a perfect run.

It appears to me that the legacy map 100% world record run by PanNic97 uses fullbright and this was accepted. Still standing 2 years later, I was wondering what were the deciding factors in making this against the rules today.

Edit: The Legacy boat% record by G_K_ also appears to use fullbright.