Nice set, I would first get the engine running.
You may want to bang out some of the large dents and leave the finish as is because this is what your Great Granmother did and it represents your family history.
Just imagine bringing this train back to life and running this train around a Christmas tree with your family.
Looks like some missing trim work and head lights need to be replaced.
Henning's or Olsen's are a good choice plus there are others as the forum members could direct you.
Loco will need to be re wheeled and this may be a good time to replace the wire to the pickup as the wire may be cracked/damage.
One Pullman car looks like the roof is dented and this could be banged out if you desired.
Will you be doing the work yourself? If not, you could always ask the forum members on who could repair this.
Price on parts could be looked up. To get the part numbers google up Olsens train Library and go into the library.
Once there, look up standard gauge loco 10 (I did not see a 10E listed) and get the part numbers for you parts. Or you couls just call Henning's.
I just picked up a Lionel 10 at a show for $100.00. It has a bad repaint , Engine was re wheeled and everything is there and it is runs.
It would be nice if you list the numbers on the side of the cars.
I m not sure of your cars as other members will give you a heads up on the price.
You could look at eBay for the price and just remember that what you see may be a high asking price not for what it sells for.
Just enjoy and get it running/have fun.