The engine oil is added by removing the engine oil cap on the passenger side
engine valve cover ( it's on the top of a metal extension tube from the valve cover
near the front of the engine )
5 quarts of oil. ( with filter change )
Change the filter at the same time and you will need 5 quarts.
If it fits it should work
5W-30 is the preferred oil ( that's what I've used in my 1995 Ford Explorer since 1995 )
5 quarts
SAE 10w30
According to the 1999 Ford Explorer Owner Guide ( 5W-30 ) is used in all the engines
My transmission change through the Ford dealership was about $2800.
If you use the motor mounts off of the 1991 explorer also, it will fit and transmission should line up if it is same size motor. If going from a automatic to a standard, you will have to replace the flywheel.
That all depends on what size engine an what year
Yes.
According to the 2006 Ford Explorer Owner Guide : For the 4.6 litre V8 engine : With engine oil filter change : ( 6.0 U.S. quarts of 5W-20 engine oil )