On the jump seats at the stern: The OB is much lighter than the I/O back there (my point of reference) but about the same hp. People love 'em. Problem is you load up the arse and you have a problem with the hole shot (getting up on plane). Several corrections for that which are prop pitch reduction, Whale's Tail (brand name) bolted to the AV plate, or trim tabs that bolt to the transom. The prop pitch reduction helps the engine to develop it's hp early which keeps the prop twisting under load. The other two are like flaps on an airplane as they force the water down at the transom (for every action there is an equal and opposite reaction....forgot the author...somebody will remind us) which forces the transom up...aka gets you on plane quicker and helps to hold plane attitude at slower cruising speeds. Money well spent and the guys that have them will probably chime in if they see this posting.
On the engine you need to tweak the prop if needed after you diddle with everything else.....all other options. Come back on here and we will help you through that tweak.
On the seats, with the high sides, you will either want a pedestal or you will be sitting on the back of the back to back when you are the helmsman. The latter being the case, you need to ensure that you get the seat close enough to the steering wheel to allow you to do that yet have knee room when you are sitting IN the seat.
Nuf for now.