Requests work exactly like you would expect. That is, a landing pad which requests something will be fulfilled if a platform can fulfill it. It is effectively a blue chest, while the platforms are red chests. Requests won't go to the wrong landing pad.

Trashing items from space platforms will just randomly pick a landing pad to dump it into. (you probably shouldnt be using trashing anyway imo, its like an unregulated purple chest)

Nothing breaks (seemingly) if you try placing pads adjacent to eachother. Which cargo bay connects to what landing pad if they are connected to more than one landing pad is determined by engine magic, don't ask me.