You've asked a very good question there, IronPriest. You've already got some interesting replies.
My 2-cents worth:
I read a wonderful editorial in an English scale modelling magazine some years ago talking about how reliant some reviewers were on published scale plans. The reviewers were bemoaning how "inaccurate" some kits were when compared to those plans, without calling into question the plans themselves. The point the editor was making was that all the plans, all the profiles, all the models are all the result of human effort. In the case of the scale plans, they are often put together by dedicated hobbyists, not unlike ourselves, who do the absolute best they can with the information available. They often don't have access to a prototype, and usually work off photos and sometimes factory general arrangement drawings. (I'll scan that article and PM to anyone who wants to read it).
The important thing to bear in mind is that NO "scale drawings" as such were ever created for these aircraft in the first place, even by the engineers. They only ever produced drawings of individual parts, and then more general drawings of the sub assemblies and the assembly procedures. At each stage, the focus was on making the important part of each drawing accurate, the rest being less critical, and more general. The mystical "Factory Drawings" simply didn't exist. I have compared factory Station Diagrams, General arrangement drawings, repair manuals, training manuals, markings guides and spare parts manuals and none of them ever had even an accurate basic overall outline! You can get almost all the info you want, but there will always be some guesswork. Unless, of course, you are prepared to spend a couple of years just on the linework.
The bottom line? Don't get too hung up on making these profiles into engineering drawings. No-one is ever going to try and build a Spitfire from what we produce here. I think of them more as "Detailed Approximations".
Having said that, I do try and make my work as accurate as I reasonably can. With the emphasis on "reasonable". When I have access to a prototype, I will do a few basic measurements and scale everything else from those. I never trust someone else's drawings as they are just as human as I am, and make the same mistakes. I verify every line with photographic reference (when possible)(and unless I don't!).
As far as drawing size goes, I do my linework at 1:10 scale. This makes all the math very easy. As far as timing goes, I keep track of the time spent on each project and the linework alone for the Avon Sabre will take 45 hours to complete. It was about the same for the A109E.
After that comes the fun part!
The most important thing is, don't get so hung up on any one aspect of this stuff that you lose your enjoyment. Focus on what you like. If you like doing the linework most, and find the accuracy a challenge, go for it. If you just want shade stuff and play with forms, go for it. If you want to depict as many colour and marking schemes as you can, go for it. If you are after the super-realism and don't mind a slow production rate, do that. Whatever floats your boat.
I'll take a breath now.
Grubby.