As to the 1/4" difference on the one wall versus the others, I don't think it will be that noticeable when the building is assembled. I can see the difference with the parts sitting flat on the table, but I would thing you will have to point it out to someone looking at the finished project before they would notice.
I can see that getting the drawing exactly right will take some practice. I think it is a pretty good run for such a complicated part as a lathe for your first try.