EEEEEEEEK a major call to my credibility
Get out and do three things, this is even before you begin to shape.
For what you are wanting go 9''
Number one ask yourself what you want the new beastie to be capable of, get a ply wood or heavy cardboard, cut that to the plan shape of an eight foot mal you think does those things.it need only be for one side, just turn it over. Do the same for a rocker template top and bottom.
They are your rough outs.
Next consider the rails they are the most challenging to get right and symmetrical at each side.
Look at the rail to rail bottom contours at selected point along the board.
There will be a progression through concave to flat to vee or rounded bottom , a newbies way is to do cardboard profiles at selected point so you can run the shape from one to another.
Now I pencil in the plan shape on the blank, and because I haven't done this I check for symmetry in the plan from the stringer..
First scary bit get out the saw and cut the shape out, keep the saw vertical ( angle it and you will undercut the deck or limit what you can do with the rails.
You can if you allowed a little tolerance cut to your line, or just outside it if not but keep to the shape!
Examine what you've done hopefully it has worked.
If you are lucky and you have agood blank, it has a good rocker and no tweaking except the bottom contouring is necessary.
The scary scary part that which really shows the quality of the shaper, the rails, you've looked at your model that you are copying now you mow from your contoured deck and bottom and also the changing progression of your rail types. Don't get excited, heavy hands here will alter your plan shape .
I reread your post and further thoughts came up!
50/50 rails heading to a slightly hard bottom edge near the tail, a fairly long flat to the bottom as a planing surface, a
slight tail kick to aid turning and maybe a very light vee to the centre fin box. (added strength) also gives a little zing to laying over for turns.
Can't advise you about outer fin plugs or boxes, only centre fin boxes had been invented when last I shaped
If you get it anywhere near close to what you are copying it will work, just think some pretty lousy Chinese boards are out there working.
You are supporting your most local shaper!
Progress photos please.
I've taken up troll hunting just for fun, instead of a rifle I'll just use a pun! 冲浪爷爷
