Hi,
Here are some suggestions:
1) Come up with an app that basically mirrors/simulates what performance any potential contractors should achieve with your rendering service. The goal for you is to check the particulars of the "horsepower" of the candidate farm under test. There are several configuration factors that may or may not be important such as employment of:
a) SSD's
b) high end CPU's
c) internet connection
d) MB idiosyncrasies
As a crude, at hand mining example using whattomine, 41 1080ti GPUS, have the equivalent ETH hashing power of about 100 1060 cards. Therefore GPU count can't be the sole criteria.
To try to avoid gaming the system you may want to spec also cclock, TDP, and Mclock of the FUT.
These are good suggestions regarding the platform. GPU mining is still profitable and anyone saying something different is uninformed or trying to keep you from raising the difficulty on their miners! Over the next 12 months and beyond the picture will become clear what projects truly believe the concept and technology of decentralized blockchains and which ones are out for greed.