So I know we're on part 4 and I haven't touched a piece of wood yet, but you can't rush these things. Everything needs to be taken into account if you want to do the job right, and that's a big thing for me on this project. In my mid 50's I don't want to have to do this again when I'm 70. That's why I've put so much into researching every aspect of this job. That even extends into what timber sizes are available from which timber merchants. I end up ordering from a timber merchant that has a wide selection of widths and thicknesses that are closest to my requirements for frame, facings, sills and glazing bars. I don't want to make this all from standard 9 x 2's. I  think I stand a better chance of everything staying straight if I'm only planing the minimum off an already straight board than cutting something small out of a 9 x 2 and releasing all the stresses in a bigger piece of timber. So with that, the order is placed, the wood is delivered. Game on.