Hi Mark, welcome to the forum.
I have a steam plant of similar vintage, inherited from an uncle. I must confess that I did steam it up when a lot younger and probably also nearly 60 years ago. The engine runs nicely on air, and will be run on steam in the near(?) future.
I would suggest that you work first on the engine. Without a lathe or mill it will take some ingenuity to remake any badly worn parts, but with any luck, carefully stripping it down, cleaning and oiling, and carefully reassembly will get that working. You can test it on air if you have a small compressor, or have a friend who can help, or perhaps at the club. You will be able to buy a few fittings to help you connect it up. Realistically, it has probably not run a lot, so there is probably not much wear. Do buy a little set of appropriate spanners. Don’t wreck the fasteners with pliers or adjustable wrenches.
The boiler is more problematic, as there are significant safety risks if the boiler has deteriorated. I suggest that for the moment, you stick with polishing that copper and the brass fittings, it will come up beautifully, and as it has considerable sentimental value to you. Maintain it as part of the display until you have more understanding of the issues. It should be relatively easy to disguise the fact that the air is not connected to the boiler. When you get to know the boiler inspector in your club, you will be able to get a reliable assessment of the boiler condition, and what will need to be done to get it working if that is indeed possible. But in any case, keep it, and polish it as part of your display.
Good luck with a great project, and an adventure in learning a new hobby ahead of you.
MJM460
Ps - I see the project has overtaken me in your other thread. But you get the general idea.