Hi, and welcome. The hoops are daunting, but if you run into a road block, there are lots of experienced folks here that know what to do. So, after having drs fail me for decades and tell me what can't be done, I'm to a place that a just get as much information as possible, and tell them exactly what I need, and WHY. I often bring printed material from pubmad or relevant studies to leave with them. They may not read it, but they will look at highlighted relavant areas. The reality is you may not get to their goal of 400, but that doesn't mean this surgery won't be life saving for you, and the longer it's put off, the worse your health will be. I'm a fairly quiet, non confrontational person, but not any more when it come to getting medical care from doctors.
I know others with the DS that take meds for bipolar, and the DS hasn't been an issue with those (some have had issues with types of staying on them, but it wasn't related to the surgery).