I agree with tobyker
The first consideration is the size of model. Over 1m can be really difficult to transport without special considerations to vehicle or breakdown of the model. Most models are 1m or under, giving a wide range of scales on the lake.
Once you have a rough size you can work to a rough scale. 1:12, 1:15, 1:16, 1:30 etc. You can work to the nearest convenient scale for parts/figures that are available. Model railways or military models are a good source, as well as people like George Turner who makes nautical models of gear and figures.
For many items on a working boat there is no scale as such. For example, deadeyes would be the right size for the size of vessel. There are a lot of scale parts available from The Model Dockyard, and they sell deadeyes by size, i.e. 3-4-5-6mm etc. You pick the size that is right for your model. Same goes for ships wheels.
For most working models, many modellers opt for a 'stand off' level of detail. That is it looks right from a distance, but would not stand up to close measuring. There are modellers who go to extremes of detail, but for most of us there is a compromise between detail accuracy, working parts of the model, costs, and build skills. The other thing to consider is the fragile nature of some of the details you may want to add.
Also rememember that for working boats, the crew often made their own tackle and bits and bobs with available materials, and so every bucket or pole (for example) could be different sizes.