Magic carpets - fin setup and rocker outline

Hi, Im a grom to Swaylocks, brought here by a newly developed obsession with making a hollow wooden surfboard. While my aim is to make a classic longboard, for the first board I have logistical considerations, not least of which is getting to my fathers to make use of some of his woodworking machinery. Add in materials use on the first try, and Im thinking about making a magic carpet, which would also add constructively to my current quiver of one 9’2". 

SO, erring towards a single fin, but still looking for consensus on the single/tri for a magic carpet. Also, could use some guidance on rocker, as im seeing that rocker is quite limited on the magic carpet. Ive seen description of a nine-plus by cutting down a longer blank. but is this by cutting off the nose section? other descriptions of magic carpet are a longboard with 2-2.5 feet cut out the middle. Presumably the blank isnt literally shortened cut-and-shut style? 

would 2" rear rocker and 3" front on a 7’0"  be about right (and retaining volume out to nose for float)

any advice much appreciated…