You do need to raise the car unless you can fit under your car while its on the ground. You dont need a new plug every time, but they recommend a new washer. I usually dont put a new one on and havent had any problems.

 

To answer your questions no, you don't have to, but it's better to do it. Get a new washer for the drainplug just in case. Is really not difficult just be careful noto to strip the plug.