Go to any parts supplier.
Do a Google search for it or buy a repair manual.
After looking at the ( 1996 , 1999 , and 2002 ) Mercury Villager Owner Guides : The fuel tank capacity is ( 20.0 U.S. gallons / 75.7 liters )
How do you change the thermostat in 1999 Mercury Villager
Yes.
I looked at the Mercury Villager Owner Guides from ( 1996 , 1999 , and 2002 ) With engine oil filter change : Each Owner Guide shows ( 4.2 U.S. quarts )
This is as complex procedure. I suggest you buy a repair manual if it is not obvious to you, and you don't have experience.
According to the 1999 Mercury Villager Owner Guide : ( 20.0 US. gallons )
You would need to be more specific with your question. You are not providing enough information to supply a meaningful answer.
In the engine.
No, no room.
134-A
According to my Hanes repair manual, it is under the dash attached to the firewall just beside the evaporator housing.