Oil drain plugs are designed to work on a level surface, but SO LONG AS you do not change the vehicle pitch enough to keep the drain plug from being at the lowest point of the oil system, it will still drain fine
If it is horizontal then I do not fill it before putting it on. The oil would simply pour out, making a mess. It is generally not necessary to pre-fill the filter. But, if you can, it certainly doesn't hurt anything and oil will start circulating a couple of seconds earlier on restart.
Add oil to the car if the dipstick reading is near the minimum line. You should top up your car immediately if you are at or below the proper oil level to prevent damage to your car. Adding oil to your car, however, is not a substitute for replacing your oil on a regular basis.
The oil will warm up to about 100 degrees, which is not hot enough to burn you, but warm enough that it will flow easily. If the vehicle has been driven, let it sit for 20-30 minutes before draining the oil
An oil leak that is left alone can cause seals or rubber hoses to wear prematurely. Furthermore, oil leaks are a fire hazard and can cause your vehicle to fail without warning. If the oil catches fire or the engine fails while you are driving, there is potential for injury to yourself and others.