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.
That all depends on what size engine an what year
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.
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 )