I think a number of posters have already pointed out a number of the challenges you face. While your plan COULD work, it doesn't sound ENJOYABLE. Here's my take:
WDW buses are rather variable and unpredictable. Your room might be close to the (first) bus stop or not. CSR is a LARGE resort, and you have to navigate with a stroller. Stroller = taking the elevator (or carrying it on the stairs) WDW suggests you allow 90 min each way.
Maybe I am misunderstanding, but when you say, "elaborate costumes," I hear a few things.
1. Putting them on will take time. Is everything laid out? Make-up? Hair?
2. Will you enjoy any of the process if it is this rushed? With a 2 hour time window, you'll (probably) have to start dressing right away.
3. Simple is good. When you say elaborate, I hear uncomfortable. Uncomfortable and WDW aren't a mix for anyone, especially if toddlers and a 3rd trimester pregnancy are part of the mix.
4. I'm also struggling with mixing costumes and 7D. After 7D, my normal hairdo looks s a bit windswept.
5. SECURITY SCREENING!
We were just at MK. If you are wearing costumes, you will ALMOST CERTAINLY be sent though the metal detectors. Before a party, I predict the line will be miserably long. At least longer than I'd want to wait. On a recent normal morning it took us 20min to get through MK security/bag check/front gate.
BOG is at the back of MK. I don't think you will be able to get through security with costumes, walk the park, and ride 7D in 20minutes.
At BOG, if you are a no show, you'll be charged the no show fee of $50.