Richie
You start your scratch build the day that I have to go away for over a week....! Now you are half way through the build and I have not been able to compliment you on your efforts!!!
I completely agree with what has been written so far - practice is the only way to learn, and the person who never made a mistake never made anything. Some seriously good advice has been offered already, but of all I would repeat what Steve (SMP) has written - write out your procedure beforehand. I often spend time thinking several stages ahead and then write down notes - just for me. When writing I sometimes have to cross things out as new ideas or possible problems come to mind. When in the process of building, the notes are a guide, not a set of instructions - be ready to be flexible.
I also find that the simpler the procedure and tools the easier the task - it is so easy to over complicate things. Frank's comment about machine tools is also apposite - I rarely use my Dremmel and when I do it is not on plastic because the latter melts and clogs the tool head. Also you have much finer control by hand even if it does take a bit longer. The comment about making your parts fit the aftermarket parts is also very good - who is going to know if your fuselage is 2mm too big because it was made to fit an aftermarket engine? As for making several parts before you get it right, my advice is that as you gain experience, those problems will markedly decrease - I can usually make something properly first time these days, but it was not always so.
With reference to frames, do you know of this method of holding things together and keeping them the same size? This was a Bleriot fuselage frame that I made in the True Scale many years ago:
It does not guarantee 100% success but in my experience I have very few failures using this method. It is simple and quick!
I intend to follow this thread closely now because you will be teaching the rest of us some useful tricks - and I for one want to know what they are. There is so much to learn in this hobby, and so many teachers!
Stephen.