15psi (1 bar) is plenty and I'd start around 5psi.

Check the oil. Hard to say how much should be in there, but with the forks fully compressed I'd guess you need ~ 200mm head space. If you want to stiffen them slightly, try a spacer ~ 20mm on top of the spring.

All estimates based on previous experience. The rebound noise could just be the fork tube hitting a stop or the spring hitting the caps on the inside. Once again look at the oil and put thicker weight oil in, say 15wt rather than 5wt. If you have no special fork oil, just use engine oil or cooking oil until you can get the proper stuff. Anything is probably better than nothing!

Good luck..