For sizing, trial and error, based on things you want it to scale well with. I settled on a standard of building the model at N scale and memorized the formula I use to convert that to Rolling Line scale, once I had the model in Blender. But, different people will want things to be different scales, so, pick an existing thing you want your locomotive to look right with, and just use trial and error to get it right or close enough to right.
For making something with only one set of wheels, IIRC, one of the wheel presets is "none." Then, I've added a third set of wheels and had that be the actual wheels of the model, with the "lock to body" (or whatever the wording is) enabled. I think you have to fiddle with the setting for which sets of wheels it rotates on, but I could be wrong.

Originally posted by Ixia Irisborne:

For sizing, trial and error, based on things you want it to scale well with. I settled on a standard of building the model at N scale and memorized the formula I use to convert that to Rolling Line scale, once I had the model in Blender. But, different people will want things to be different scales, so, pick an existing thing you want your locomotive to look right with, and just use trial and error to get it right or close enough to right.
For making something with only one set of wheels, IIRC, one of the wheel presets is "none." Then, I've added a third set of wheels and had that be the actual wheels of the model, with the "lock to body" (or whatever the wording is) enabled. I think you have to fiddle with the setting for which sets of wheels it rotates on, but I could be wrong.

The third wheel set trick works, thanks for that.
I don't quite get what you mean with building at and comparing other scales for getting models right, I just want to shrink a model that's currently the size of a blimp down to a normal 0-4-0/0-6-0 locomotive scale on the game's tracks. But as you say, looks like it'll be down to trial and error until it's the correct size.