Depends a lot on what the game play is like. How often you move pieces, etc.

Often. There are up to 6 movement phases per turn, although every unit moves only once per turn. There will also be lots of casualty-moments, so the number of units will change as well..

Will stacks often move as a group?

That's up to the player, but I would say so.

If the stacks often move together then stacking them should be fine. If you were constantly splitting and merging stacks, that would be a pain.

Yeah I think they often move together, although you do often need to remove casualties from the stacks.
Merging might happen more often than splitting as far as moving goes, but if there's enough space in the territory, I suppose two stacks of the same unit type don't *need* to be stacked.

So what would you suggest now?

I'd suggest you release, critique, rewrite, and crudely playtest the rules for multiple iterations.

Yeah I really don't have anything to add until I see the rules...

I will. That's not what I meant with the question, but on hindsight, the question is redundant and vague.

I was still talking about the best way to stack units, to be clear.

As I've said, it depends on gameplay.

"I was still talking about the best way to stack units, to be clear"

Securely. With lots of stacks, especially if they are more than two or three high, your biggest nightmare is someone jogging the table. Re-assembling them is a pain but the worst case is you are not sure which stack a marker belongs to.

Maybe I could use the 3 -printer to create models that can be 'clicked' on top of eachother..

In the long run, yes. But don't get hung up on that for play testing.

I think you'll find the resolution of your printer is not good enough for that.

Probably.

Suggest you take a flexible approach: don't require units to be stacked just do it when the size of the territory requires it.

Yeah that's my thought. I think I'll just get enough models and be sure to have a plan B if it doesn't fit.

Still need to figure out what exact sizes I'll be using..
What's the smallest size that will not be too small to move around?

I'm at roughly 9mm wide for an infantry unit for instance, would that be large enough? Can it get any smaller?

I wouldn't get any smaller, people with fat fingers may find it tricky to move and stack/unstack them with the result that they send pieces shooting across the board. Size is something you can learn about from testing.

Whatever you fix on, suggest that you have the same size for all units to facilitate stacking if necessary (resources might be different to allow easy recognition).

The physical aspects, as much as the rules, are something that testing will help you get right.

I'm having trouble finding an artillery piece.. got the rest excluding resources.

As for resources, can't think of a nice way to represent aluminium..

What are the other resources?

Gold, Iron, Oil.

I was wondering about a drinks can but that will be too close to an oil barrel.

I found this picture of aluminium billets:
http://www.constellium.com/var/constellium/storage/images/media/images/aluminium-billets/42574-1-eng-GB/aluminium-billets.png

so would a pile of cylinders work?

I was thinking about tubes, so either one of those will probably do.. Ironically though, I think it will be hard to find a 3 model for that because people are just too creative for a simple pile of cilinders..
Don't know how to make one myself, will keep looking and otherwise figure out how to design it myself.

Just go for a triangle

I suppose I just think too hard occasionally..

So now I just need to think of a way to find an artillery field gun or something like that which is printed in one piece. I think this may be another case of me thinking too hard but I'm just not finding it.