I've never experienced any side-to-side issues with mine, in fact find it extremely stable with it's 9' beam. I have had some bow bouncing due to (i assume) the weight/locations of the outboards vs. an I/O. I usually end up running with my trim tabs extended which solves the bouncing. Overall...
I had the Ivory interior on my 250 SDX OB, and I went with Stone on my 290. The Ivory was a pain to keep clean, the Stone seems much more forgiving from a maintenance perspective (make sure to use a protectant like 404). I live in Florida, so the vinyl can get hot if the boat is just sitting...
I think the Pump out is worth it when you have a large holding tank such as the Vacuflush. But to install it after the fact and only use with the porti-potty which is a very small holding tank seems like overkill. My last boat i converted the pump out porti-potty to a standalone so i could just...