1, the harness is included in cars where they have seen repeated failures of the stock plug. so that needs to be done on cars that come come with it. and you cant use splices or any other type of crimp, they need to be soldered well and heat shrunk.
2 you can remove either the fuse or relay either will prevent the pump from turning on
3 not sure what you are talking about, but if you replace the filter make sure that you put a pan under it because the gas is still in the lines
4 i normally jack the car from the middle in the back, most cars have a raised flat piece of frame between the rear control arms, then put jackstands under the frame on both sides
1998 Bonneville SSE
2007 Monte Carlo LT-KYB, Clarion, Polk audio, Kicker
1999 Yukon SLE-KYB, Air lift, Reese dual-cam, Tekonsha
1987 Firebird-355/th400-nothing stock