John,
While this is not step-by-step instructions, and the model version of the Edwardian launch does not seem to be specifically included (probably because the model plans for this one were only produced at a later date) there does seem to be a Model Boat Building in Wood manual available, written by Paul Fischer of Selway-Fischer Designs.
I have not seen the real article for myself, so cannot really comment on it, but on the web page linked to above, there is a table of content and some sample pages to look at.
In the end you are the one best placed to estimate your own capabilities for tackling a scratch build project, as you know what level of time, determination, experience, tools and other resources that you can draw on, and of course anything can be tackled if one really wants to and is prepared to put in the effort.
That said, I, too, think that the previous advice in this thread is very sound: a not too complicated kit is very likely to get you off your marks that much faster, to considerably facilitate bringing your first project to a successful conclusion, and to allow you to find out for a reasonable cost in time and money both if the hobby is one you enjoy, and how easy/difficult you find it.
Good luck and have plenty of fun 
Mattias