Okay, so I fully acknowledge that this is probably a remarkably dumb question. But I just want to check to avoid ending up with a cake wreck, so please humor me.

If I'm using a styrofoam dummy as the bottom tier of a 3 tier cake, the styrofoam should be able to support the weight of the real tiers on its own, right? I didn't plan on needing to reinforce it with anything. Is that right? I've googled cakes with dummy tiers and there never seems to be any mention of reinforcing them. But the last thing I want is to assume it's fine and then end up with it buckling under the weight and leaving me with a ruined cake.

Yes, the dummy tier will be strong enough to support the top two tiers.  

Thanks Sandra!

You are very welcome.  The styrofoam dummies are very sturdy.

One could always check something like that by standing on it

Lol, maybe stacking books on it would be a safer option, Lynne!