This may sound dumb..but how would I cut into the castle cake? Would the top tier be on a cake board...therefore would I take top tier off and cut pieces that way...or would it be sturdy enough to cut if it's still on the bottom tier? Sounds dumb but I'm new to the stacking/doweling thing...thank you for any help.

There are no dumb ?s If you don't know the answer you have to ask someone who can answer it.
There are many different castle designs. Most are tiered cakes. That means each tier sits on a cake board so yes, you would take it apart. Basically one would cut it like a wedding cake.

I think it depends if it's sturdy enough, I never separate my tiers to cut, but my higher cakes are 3 tiers only and I use 5 big fat dowels on each tier and works perfect for me, (since I cut the cakes must of the time) and I try not to put a ton of pressure when cutting just enough to cut the cake. HTH

Thank you both for your help. This is my first 'big' cake and with everyone watching I wanted to make sure I cut it the right way.

just so you know...i've thought of questions like that too!!

I'm making a lighthouse cake, and i'm not really sure if i should cut into the lighthouse first or the base!!

Well, I'll think the lighthouse will be taller than 3 tiers, you will need to take apart the tiers before cutting it, I wouldn't risk it with a very tall and narrow cake.

Oh, I tought it'd be a tall cake , then you should not have that problem, as I said, I never take my tiers apart and it's been fine up to now (hope I didn't jinx it)