Hi Phill,
Personally I would go 3..

The plate will help kids right the boat.. Its easier to haul ones little body across a plank just above water line than a slippery hull.
Saying this I would see a reasonably stubby plate design not a ultra long wing. Then a piece of glassed shaped piece of ply would be sufficient.
Kick up rudders are fine but again reasonably stubby rather that long thin foils.. The windrush cats do reasonably well with their spades so I'm not really concerned one way or another. I would also look at parallel sided plates and rudders.. This would be easier for home builders to make.

If your thinking OD.. I would suggest looking at a cloth strop or device to keep the main from looping and catching on a wee laddie or lassies throat. The main pictured while great for the experienced skiffy isn't one for a kid who lets the main loose and thus slack when gybing!!

Just my thoughts.. <img src="http://www.catsailor.com/forums/images/graemlins/tongue.gif" alt="" />