Thanks for the expanded discussion of your plans, Max. I hope I didn't come across as insulting your ability to use a straight edge! 
It's quite interesting to read of your compromises and decisions. Having those windows for a double-height first storey now makes sense. Several of those "googled" photos seem to show lots of large glass windows facing water. It's both suprising (heating cost, potential for wind damage) and sensible (good light, stellar view).
I dunno that you'll be missing much without the lean-to shed. It did add some character to the original, but as you say, you've got interest in varied window placement and sizes, stairs, and landings, etc.
Keep those photos coming.
TRRR
