It's been a while since I made this design, so dont really remember all the print details. If I remember correctly it was supposed to be printed separately and snap (thigthly) in place, but might work better with print in place. I think you need supports, but it should not be needed in places hard to reach. As for infil, just use anything, but make the wall perimeter high enough so you only really get infill in the bottom part. You probably want a stiffer type of petg of some sort, as pla might be to brittle, but it needs to be rigid enough to hold the lever. Also make sure you have good enough layer adhesion.