Three questions above, one answer. The short version if you want to skip ahead: indoors or general outdoor → Neoprene. Sun-baked outdoor → EPDM. Oily or fuel-exposed → Buna-N (Nitrile). Over 250°F or under -40°F → Silicone.
The reasoning behind every recommendation is on the rubber compatibility chart (all four compounds across seven exposure types) and the material & durometer guide (Shore hardness explained). Then shop by part: grommets · washers · O-rings · edge trim · rubber feet · vibration mounts.