Glen,
G'day
Congratulations on upcoming teacherhood
I don't know if the title has to be awarded by Martin - but I would vote you a Great Antipodean Planker (GAP)!
Also the first planking looks very neat - don't beat yourself up over ridges, etc so long as they don't throw the second planking
If you need to sand - even right through - it isn't a big problem - just add patches on the inside (balsa planks or sheet) and carry on to the second planking.
Your drilling idea is good - can I add a suggestion that goes with it? (Nicked for Harold Underhill)
Instead of pinning - use bamboo treenails to hold it all together (he dips them in "knotting" as a glue - I would suggest PVA or balsa cement) Then cut off ends when dry with nail clippers or sidecutters and they will look like the treenails they are! Super scale!
(I can offer a fast way to reduce barbie skewers to 1mm bamboo dowel fast if it would help)
Drainage of deck - both your plans would work well - but scale water is not available - and the larger the freeing area the better to
clear the decks.
<<will my drop keel be deep / heavy enough for the job, or do I have to redesign it>> Suck it and see! It will certainly work for (up to) some wind speed. If you need more righting moment - drill a couple of holes in the bottom of the keel and bolt on a lead "stormweight" >.
<<how much longer can I put off the purchase of below decks servo winch and running gear? Not long I suspect...>> True
<<how will I fit the rudder servo so that the push rod can't be seen above the deck? Tricky, as the stern end is shallow and solid.>>
I believe that your rudder post is angled - use ballljoints for connecting to the servo. Move the rudder servo forward till you can (just) reach it and the linkage through your deck access. Make the pushrod stiff enough to avoid bending when its pushing - bit of arrow shaft or 10mm dowel from the hardware store.
You could, if necessary operate the tiller above deck (it does have a tiller, dunnit?) with cables in scale fashion using the servo as a winch with a drum.
Best idea might be to fit a small double ended tiller under the deck (even if you have to recess the solid a bit) and use two cables in pull/pull format to operate the rudder - this only needs a sliver of space. If you do this make sure that the servo horn is exactly the same width and the rudder arm and use nonsrtetch cable
Keep up the good work, collect your scroll, keep us posted and enjoy!
andrew