Dan,
I would rennet a whole lot closer to the 0.1 drop in pH rather than the 0.5, especially considering the rapid acidification your experiencing with your farmhouse culture. Don't press too hard too quickly, give the whey a chance to drain out as you increase press weight, and the curd acidification is an integral part of that process. What I am trying to say is that press pressure alone wont drain the whey it's a combination of factors, and cheeses in this category aren't very hard pressed normally. I don't know if you are pressing too hard too quickly but I'm wondering if that might have been at least a part of the problem with your cheddar. I don't know how you are drying your cheeses, but, here is what I do. I have a sterlite tote that I use only for draining and drying cheeses. I elevate a drain board (not so important with a pressed cheese) with a drain/ripening mat on it and let the cheese dry at room temp for a day or two. This protects the cheese from dust, bugs and what have you and prevents it drying too quickly, you want a humidity of 85-95% through the whole process. Washing the rind should only be done after there is a rind to wash, the vinegar/salt water rub is really only to deal with the occasional spot of mold that might appear. This kind of wash can be very drying to the cheese rind as counter-intuitive as that is, at least that is what I remember Yoev (iratherfly) has written and I tend to trust his word on these things. He actually recommends salt rubs after a good rind has formed (depending on the variety of course), kind of like dermabrasion for cheese, and the salt wont be absorbed by the cheese once a good rind has formed.
BTW, what kind of cheese is this going to be, other than washed curd you didn't say?
John