Jane,
I agree with David. The Kasten designs surely look sexy, with their detailed drawings, but I question how practical they are. I don’t find any of them on YouTube.
The junkrig on Shackleton also looks more elegant than practical. However, if there already are boats of this design out there, sailing and sailing well, I will admit that I was wrong.
I also wonder about the position of the cockpit. That space would be very useful in the (fore) cabin, while it looks to me to be a terribly wet place to be in, if used as an open and unprotected cockpit.
Remember, there is also another alternative to building: Convert a second-hand boat to JR instead. Converting a boat to JR may take a year, while building a boat of this size will keep you grounded for three to ten years+. The question is then, do you want to build, or do you want to sail?
I don’t write this to discourage you, I just want you to get out sailing as quickly as possible, and thus learn what it is all about. After a season or two in a junk-rigged Coromandel, Westerly or whatever, you are much better prepared to make a qualified choice for the next boat.
Anyway, good luck!
Arne