You're talking about 3D thinking but then you mention setting up a digital canvas and those are kinda different skill sets. If you want think about a space in 3D, the easiest way I've found to do that is just take advantage of occlusion. The simple act of putting one object in front of another object is the first, easiest step to making a space 3 dimensional. Break your space into a basic fore>mid>background. Work back to front. Place things in front of other things (and use that to frame your focal point). Contrast those layers against each other with scale, tone, line weight, colour.

In this piece, I'm just going: okay you know how big a tree is. Put that in front and it immediately lets a viewer know the size of the space because they have an idea of how big a pine tree is. They know how big a bird is. A power line. Foreground is black. Midground is dark grey. Background is light grey.
This might be too simple an answer (I know you're a relatively experienced artist, from a brief look at your profile), but Bob Ross is genuinely teaches a great way to start thinking about how space is constructed. He never uses grids, he's just putting one thing in front of the next thing.
When I set up a piece, towards the beginning, I put together a really simple 3 or 4-tone block out that is like: here is the close, middle and far part of the drawing (the distance between these can be really long or really close) and use a dark, light and midtone to be each layer. If you have a bunch of architectural elements to deal with you can apply the rulers and grids after that, but your eye is a pretty good judge otherwise.
Does that help at all? I hope?
