Nice train set you have.

First thing to do is get a large box of cotton swabs, a can of Naphtha, and a single edge razor.  Use the razor to scrape off any built up gunk on the wheels, then use cotton swabs dipped in Naphtha to finish cleaning up the wheels. Clean the locomotive center pickup rollers the same way.

Get some light oil to oil the axle bearings, and grease for gears. Labelle makes products specifically for model trains.
https://labelle-lubricants.com/model-train-lubes/

Olsens has a website with service manuals for much of what you have:

6250 NW-2 switcher - http://pictures.olsenstoy.com/6220-50.htm
2328 GP-7 Switcher - http://pictures.olsenstoy.com/2328.htm
6460 Crane car - http://pictures.olsenstoy.com/searchcd31.htm?itm=551
6511 Pipe car - parts list - http://pictures.olsenstoy.com/searchcd31.htm?itm=440
3469 Dump car - http://pictures.olsenstoy.com/searchcd31.htm?itm=524
397 Coal Loader - http://pictures.olsenstoy.com/searchcd31.htm?itm=297
395 Floodlight tower - parts list - http://pictures.olsenstoy.com/searchcd31.htm?itm=296
3656 Stock car - http://pictures.olsenstoy.com/searchcd31.htm?itm=545

The rest of your trains should just need a good cleaning and lubrication.


Larry