Thanks, there's plenty to chew on here.
For me, there's another complication... I have a small machine shop and can do electronics too. Oh, and CAD and I do a lot with industrial grade 3D Printing, including metal parts.While I won't be tooling up a set of metal tracks, I could do my own gearboxes and a number of other things. Likely cost me more than buying, but I'm one of those who likes the building maybe more than the running!
We'll see how deep I get here...

p.s., in case you think 3D Printing is just that junky home printing stuff, take a look at this engine I did... even the brass is 3DP...