Hi Chris, Welcome to the world of model boats. Funnily enough I am also into model trains and have a number of your figures scattered around my OO gauge railway layout. I suspect I may have also seen you at one of the model railway shows doing your scanning.
As regards model boats the following tend to be the more popular scales:
1/12th, quite a few kits out there are 1/10th and modellers populate them convincingly enough with 1/12th scale resin dolls house figures. I have a 1/12th scale steam model that has around six or so "passengers". You can't get ones with outdoor clothing though so there is definitely a niche there!
1/35th and 1/32nd, probably more kits in this range, some with white metal figures included. Good quality resin options would be useful to many modellers particularly in the areas of period fishermen, officers and sailors.
1/48th, a very popular scale with quite a few warship model kits in this scale. Consequently RN officers and crew, gun crew, sailors etc would be popular. As well as suitable period crew for tugs, work boats and fishing boats.
!/72nd, some models in this scale but not as popular as the larger scales.
1/96th, quite a lot of warship kits in this scale so RN officers, gun crews and sailors might prove popular.
1/128th, probably too small to consider anyway.
They are probably the more popular scales although I do know of models in 1/16th and 1/20th as well.
Just a final word, knowing both the model railway world and the model boat world I think it would be fair to say that the model boat world is a fraction the size of the market of the model railway world. As comparisons, the model boat world has only one magazine and sadly due to a cancellation there are really only one or possibly two shows this year. Consequently the demand from model boats will be significantly less than you will be used to from the model railway quarter.