Welcome to the forum! I second BMORAN4s sentiments, you have a fantastic set in exceptional condition. As it is/was your grandfather's set, monetary consideration is likely secondary. However, as you mention that you are relatively new to model trains, it should be said that after a quick review of eBay prices, you are looking at roughly $2,000+ value between the locomotive, tender, and passenger cars. The condition of your pieces appears to be very good, which really drives prices upward.
I say this just to make sure you are aware of what you are dealing with. Also, if it has been sitting in a box for 50 years, it will likely have hardened grease around the worm gear. Hard to say, but the motor brushes and commutator may need cleaning as well to ensure that it runs nicely at appropriate voltages.
I second REDJIMMY1955's comment of taking it to reputable train shop, professional, prewar collector, etc that is familiar with working on these. I have been messing around with Lionel trains since I was a little kid, and without a doubt, if I had one in this condition, I would take it to a professional for cleaning and lube this first time. I would ask to watch over his shoulder as well - 1 to get an education, and 2 to ensure nothing is scratched, dropped, bent, etc. After this initial cleaning and lube, you can then perform light oil maintenance as needed yourself, no problem.
If you ask on the forum for a reputable repair shop, person, that is familiar with a 763e in your approximate location, you will likely get some very good recommendations for the appropriate person.