Just my opinion , it does not hurt to periodically check the differential to make sure it is not milky because of water but the jeep is an off road vehicle and for all intents and purposes was designed with that and many other possible scenarios to happen. Don't be afraid to enjoy yourself and have fun. The fuel pump is protected inside the tank. There are vent tubes for the fuel tank and differential that should be well above the height you described. Especially with the fuel system if you have crossed the line with it , you will know pretty quick. Water is not to bad if it is an in and out situation in most cases but if you were stuck under water for an extended period you would definitely need to a maintenance check off as soon as possible. There are some educational post on this site about not trying to restart an engine that has stalled while the exhaust system is submerged. Find them and study up on them , they will save you thousands of dollars. Have fun, just putting my two bits in.