It sounds a bit like you're trying to squeeze in some milkrun instead of taking a base that's actually ready to fight with some degree of opposition. In fact, it would seem pretty easy for you to send most of your force against one target, then milkrun an undefended target with some NOE attack and wave the victory flag. Or, we split our forces into thirds (to cover three bases) and you still have 3-1 odds at the base under attack. I don’t really think that is acceptable. As it is, your organizational skills should be able to overcome our gaggle of furballers in a H2H fight if you can execute and the defense fails to execute. Or maybe you can’t take a base if it is ready and the odds are somewhat even? If so, no problem there, just admit it and well not bother with this “event,” just up and look for a fight, even look for the mighty BoPs.
[or, we do it your way but instead of focusing on one base we focus on stopping the assault in general. It's just too easy to "game" a single base using your approach.]
As to spies, frankly, I can't imagine anyone posting against horde gameplay going to the effor to spy (except for that shifty Lazs). I actually don't think they would care all that much if you bothered to send spies to our little meeting. Anyway, it's all about execution.
Charon