1992 Cadillac Deville

You'll want to get 12-13 quarts to be safe. Check the level after driving and temperature is at operating level. Then check dipstick with engine running. 2 gallons may be enough but it is worth getting another quart to top it off. Better to have it on hand rather than it be low. Depends how far you live from parts store. Don't drive it more than a few miles before checking it and if fluid is not on stick, I would get someone to take you to get fluid.
As far as the oil pan, removing the bolts is all you need to do. The bolts should be tightened in a cross pattern starting from the inside out. The torque is in inch-lbs, so it does not take much to have the bolts tight enough. Use threadlocker on the bolts. If you overtighten the bolts the gasket will get squished out the side and possibly leak. You can use some silicone, just a thin layer, to ensure a leak free seal.

You might be able to get away with dropping the sub-frame and raising the engine and trans with a jack.
It is not easy though as the springs will need to be un-compressed and you will have to dis-connect the brake lines or just drop the calipers to avoid damaging the brake lines.
The who;le reason is that the oil pan is such a tight fit against the subframe it has to be pulled off and the manifold might have to be removed to pull the engine.

Itchell labor on the engine oil pan is 1.9 hours. It can be done with the right side of the engine jacked up.

Jack it up using a block of wood under the oil pan then suport it from the top with a chane and bar suport it when its up in the air.