Newbie with a Lionel set: where to start to get it running again?

Others on the forum can provide a better value assessment. You can use Greenberg's pricing guide, but my experience says not to expect the prices listed.

As far as getting this operational I would first start with the transformer. Check that the plug wire is still flexible and has no cracks; if it does you will need to get that replaced. You should also check any other wiring for uncouplers or power to the track for similar condition. If the transformer wiring is OK, plug it in and use a multimeter to check voltage changes smoothly when you adjust the handle. If there are issues, most can be fixed but you may find it easier to purchase a new transformer.

I would then check the steam engine. Having been in storage this long almost guarantees dried grease. You will want to completely disassemble the engine to clean everything and put in new lube. Since the engine may not have been operational, you will need to look at pick-up rollers, wiring, motor brushes to see what may need replacing.

Once you do those, clean the track and see if you can get the engine moving.

Some of your family Christmas memories parallel the Lionel steam freight set 1533WS from 1955 (2055, 6026W, 3562 yellow barrel car, 6436, 6465, 6357), overall value will depend upon condition, especially the boxes. There are many ways to start depending upon your long term goals; at least as a safety precaution, test all electrical components, and if no shocking developments, set up a test track to see what is operational or non-operational. It will be fun and addictive, so start testing and cleaning. "Good Luck!"

As KENJR noted, you can purchase price guide to determine value (without any expectation of actually getting those values should you sell) but a faster, more reliable gauge of value can be had by pursuing the Sold listings for a given on eBay. That will give you a much better idea of what those pieces are selling for…

Let the fun begin. Take your time and go over each piece. Check the transformer for damage first. Clean and lube the engine and see if it runs. If nothing is broken these older engines can be brought back to life and run as they did off the assembly line. They last forever. Seeing that the set is an heirloom I’d say it’s priceless. Plenty of help is right here on the forum should you need it. Please update as you move along. Good luck. 

In addition to what Ken said, my experience with Lionel locos of the era is that the E-unit levers will loosen over time,  making for erratic performance.

Good luck and keep us posted!

Mitch

If your set is a 1533W, the 2007 guide for Sets lists $425 if it is in excellent condition.  Condition is everythin.