i am interested in the same thing! a small bitcool immersion setup for 1 S9. what is the brand/model of the pump you are using? it has to have specific viton seals for it to be compatible.

i have not done it myself yet, but i think you can and should OC as much as you can (within cooling & dont forget power limits)
you might as well!

from what ive read the fluid lasts a long time and long term effects should be nothing, since the fluid is designed to be compatible with the materials in the asic. (i have read some incompatible fluid/materials will cause capacitors to bulge and become destroyed).