Pic 3: Lower gun deck. This is the trickiest deck to plank and sand, since access is hindered by the overhanging formers. It's worth looking at all the walnut strips provided: in my kit they were extremely variable in colour and thickness. Select some that are the most similar in colour and thickness for each deck and results will be easier (less sanding) and also better-looking (same colour). Don't worry unduly if you can't get a perfectly smooth result under the overhangs - it won't show in the finished model.
See those long thin strips running through the formers in little slots? I thought they were just reinforcers. They are not - they provide the fixing for the 'tenon' cannons (the ones that don't sit on a carriage but are just pushed into holes for effect). I placed some of these strips high in the slots so they would help hold the deck, a mistake. It meant that, far in the future, some of my tenon cannons would 'miss' and it called for outrageous cunning to fix them.