What to do about a cake for 100 people?

My brother has his grad party coming up and I am at a loss as far as the best way to make a cake for just over 100 people goes. I am thinking of getting the Wilton half-sheet pan (12x18) and either stacking them (one on top of the other) or putting them side by side. The only other large cake I made was a half sheet for my son's birthday last year, and it was a bit of a disaster (it was my first large cake and I didn't have the common sense to trim and frost the edges of the sides I was sticking together.) Here is my thought: either just the double layer cake that would be 12x18x4 with an edible image, or the full sheet (18x24x2) with the Wilton graduation cap on top... What do you guys think would be best? I'm quite nervous about the whole ordeal and will definitely be making a 'smash cake' beforehand... I've read a whole bunch of tricks and tips (parchment paper for sticking, inverted flower pins in lieu of a heating coil, etc....) so now it's just the architecture of the cake to worry about! If anyone has other tips for NOT ruining his cake too, it would be appreciated!