Not sure I understood your point about channels. what I meant is to create channels that are seen only by the "org" or "space"?

I mean by default you can't set limit that some channels should be bound to the one org or group. So set the limit to create only one channel it would be a good motivation not to waste this opportunity.

Also, is there any limits for how much spaces under spaces (child spaces) are created?

No, there aren't.