In my experience, USUALLY the even numbered roomettes are on the right side of the train on Superliners. But, as noted by previous posters above, it's not guaranteed to be on the right side. One never knows if there was a last-minute swap out of a sleeper and whatever direction the replacement was facing. I've also learned that whatever is the easiest solution to move a car from here to there is how it's done...ie, running through a wye to reverse the car is not likely.
As far as a specific room number request, when booking online, roomettes seem to be assigned in order from #2 on up (#1 is the attendant and is next to the upstairs toilet). I'm unsure whether the 'automatic' booking system fills one sleeper then fills the 2nd, or if they 'ping pong' from car to car assigning #2 in each, then #3 in each, etc. I've also learned that the earlier one books, the better the odds of getting a specific roomette number. My preference is #14, lower level, next to the family room. Why? Almost zero traffic passing my door and the toilets and shower are easily accessible. However, I've also discovered to my chagrin, that not all Amtrak agents are knowledgeable in selecting a specific roomette number and say it can't be done. I recently booked my April vacation on 7 trains and got #2 in the two trains with Viewliners, and #14 on 3 Superliner trains. The other 2 trains are NEC Business Class. The agent had little difficulty selecting specific roomette numbers for me.