I've been doing cakes for years, and, if I do say so myself, I do beautiful work.
I only SELL wedding cakes; there's little or no money in smaller cakes and they take almost as much time. Wedding cakes require a good bit more organization, but once you're good at it, they go together fast and they require no color changes in your icing, no plastic pieces, etc. Wedding cakes aren't really complicated; they're just big.
My advice:
Invest in 4" deep professional Wilton pans; they're expensive, but the difference in the height of the cake is impressive. You'll find that your cakes come together much faster if you're not putting together two 2" cakes, and you'll eliminate the problem of the "bulge" in the middle.
Never touch a cake mix -- even if you add sour cream or whatever else, it still tastes like a cake mix, and much of my business comes from the TASTE of my cakes. We so rarely today have a real, honest-to-goodness, from-scrach cake that it's a real treat. ONLY White Lily flour and Crisco shortening, but sugar is sugar is sugar and store brand butter is just as good as name-brand (but never use margarine, and especially never use that spread stuff). I make my own homemade vanilla extract.
Learn to make your own homemade fondant (if you're into that). You'll be impressed by both the low cost and the quality of the homemade stuff, but it MUST "sit" for 24 hours before you use it -- if you try to use it right away, it'll fall apart. I make fondant in marathon sessions, then store it in a double ziplock; it lasts forever . . . well, almost.
By the way, I'm another cake decorator who no longer likes icing! It's not just that decorator icing is mostly Crisco -- it's the taste, the smell . . . no thanks. But I do like the cake inside!