The hardest part(after planning) is always starting. It always seems that after you get started, things just start coming together quickly even if that is not actually true. I can remember when I had started on my HO layout in my teens, it started slow, but once it was started, it came together quick.
Weird houses seem to always be the case. We've been trying to get things done on my late mother's house and the person doing the work has said the same thing about no straight lines, no right measurements, the works. This sort of is the case with houses built in the 1800's I suppose, just don't know where in the 1800's but what also doesn't help is the add on's on it.
Good luck Alex, hope to see progress come quick and hear the distinct sounds of steam as well as see the smoke. 
