Boat and engine now ordered :)
After much agonising and far too much reading of spec sheets, and after swinging this way and that between the floor options and sizes, I've finally placed an order.
3.1 metre Zodiac Cadet with the plywood floor.
9.9 hp 4 stroke Mariner.
Stainless launch wheels.
Of course, I am aware that you will all now think I should have gone for airfloor and a 2 stroke, 4.8 metres and 30 hp... but it seems the best fit.
On the water, I will sometimes wish it was bigger, but in the garage I will sometimes wish it was smaller.
Thanks to all of you who have answered my questions and offered advice over the last few weeks.