Martha Stewart's Swiss Meringue Buttercream and Basic Yellow Cake

9:48 a.m. post: I woke up this morning at 7 a.m. with an urge to try to bake one more item before I jump on a jet plane at 1 a.m. tonight. So I looked up Martha Stewart's website and came to this Crushed-Candy Wedding Cake. It looks simple enough so I gave it a go.
I have some questions that arose as I started making it: (i) what is considered "fluffy" when mixing the butter with sugar? (ii) when I'm mixing the flour and milk in batches, should I make sure they are completely incorporated before I do the next batch? (iii) when fluffing the egg whites, what is the difference between "stiff but not dry"?
Any way, I used only half of the portion for the recipe as I thought the recipe would have yielded two cakes (with an 8inch pan). Putting it in my 8inch pan, it filled it only half way. Disappointed because I wanted to start working on full cakes. I might try to turn this one into layers. We'll see.

Goal today is to assemble this cake, without the candy. Assuming the cake turns out ok, the focus will be on getting the frosting to look pretty. It should be cooked in an hour and I'll let it cool for a bit. Stay tuned...
10:25 a.m. post: Do you think if I put a dip in the middle of the batter it'll rise a bit more flat? Hate the idea that I need to flatten it and waste some cake...

I know the baking tray is ghetto; should not be using a cheesecake pan but it's all I got so far. Will pick up proper trays in due course. Now we wait for it to cool.
2:30 p.m post: So I just added a crumb coat and put it in the fridge. The icing was really hard so I softened it by mixing it around, then I found that it was almost melting like. So I think there's a middle ground that it has to be worked with. I made one crumb coat thicker than the other. We'll see if it makes a difference at all. Have cut the cake in half - will play with styling a bit, I hope.
11:00 p.m post: I finished the cake today but really messed up the icing. I should have kept mixing in the butter at a really slow speed. I sped it up towards the end out of impatience and it clumped up. This is how it looked like when it went in to the fridge and it never got better:

I kept making the cake in any event. I straighted it out, cut it in half and then crumb coated it. The frosting really was horrible to work with but I tried to keep working with it. I think I beat too much air in to it.

I frosted it as best I can and gave up frosting with the second one. So I piped it. It tastes delicious though it doesn't have the greatest frosting. At least I didn't give up!

I think the pipped one looks very pretty!