[tsubaki]

Welcome to the site.
The jackplate is to your preference, usually they are prepositioned as to the amount of setback and rise needed with several holes for most any mounting circumstance at the transom and motor ends.
Mine is the standard 5" setback and powered. I couldn't imagine not having one on this boat, it gives a lot of flexibility for maintance but I haven't used the boat yet to see about the performance capabilities (think I just got all the bugs worked out last week).
If you don't need the 12" one just go with the 5", you probably wouldn't have to change the steering and controls that way.
Good buy on the boat.