Pilly

I just inherited my grandfathers house. It is approximately 1500 square feet with 4 bedrooms, laundry, bathroom, kitchen and living room and complete upstairs that is very large and is the whole length of the house and half as wide. It was built in the early 40's and moved 10 years later to the location where it now rests. The front part was an old school and when moved my family built the back part on between 1960-1970. The house has beautiful antique pine flooring in the front and antique oak in the back part. My question is how long will it take to sand and refinish that much flooring. Should I use the same grit sandpaper on all the wood. I know that pine is softer than oak and didn't know if I should use different grit on the softer vs. the harder. Another question....my dad told me the floors were OILED back then to keep down dust and make them shine. The floors were sanded and refinished in the late 60's and they had trouble getting the stuff they used to stick because of the oil. The boards were 1 inch thick before the first sanding. The oil has absorbed into the wood, how deep and how much should we sand off?? Will this oil come off with sanding as I am afraid the poly will not stick to the wood otherwise. Will all of our work on these floors be in vain or can we make them beautiful again? Last one I promise. The floor is really drafty as there is a basement underneath the house. The air from the basement comes up through the floor. Is there a way to seal the cracks without having to go through even more time consuming work or is there a simple way to do this? Will the poly settle in the cracks and seal it?