I'd also be worried about cleaning the barrel after a primary fermentation.
I wonder what the farmers in Belgium did? That is really the question that encompasses all these questions. Or maybe the answer that answers them... whatever. Regardless, I am not worried about reusing the barrel. My plan is to turn it into an end table in my future bar shed/man cave.
Oh, I didn't realize this was going to be the last time you use the barrel. Well I guess just go for it then.
Have you thought about the grain bill? Golden Promise will work great. If you are going for authentic, you should probably find some unmalted local grain to throw in there. I live on the west end of the Palouse so it's pretty easy to find wheat, but rye, oats, spelt, triticale can all be found in my local health food store.