Hi, Jane
design brief is a little unclear
5-8 design assets??
from what concrete elements this assets should consist?

Hi - concrete elements include the lion and Supply name. Everything else is up for design.

HI, do you need textured / grainy art?
like Deus Ex Machina examples and Jolly Roger t-shirt example
Whereas your website leaves sleek, futuristic impression.

Do you need designs that are much different from base logo --- like Deus Ex Machina variation examples?
or similar to base logo --- like Jolly Roger 4x4 skulls

Contest Holder isn't always aware of how much designer wil get as a prize

on the part of designers Payments looks like next
1st Place -- US$150
Participation Payments x4 --US$10
Total -- US$190

for $150 (actualy $127.5 -- because of designcrowd fee - 15%) you can't expect 5-8 complex(mid-complex) assets, only simple ones.