I'm not much further along than you...which basically means I've been reading a little longer. No hardware.
Irising nozzles sound great, but I can't see a way to make them practical. It'd probably be easier to just have two nozzles. One for course, and one for fine.
As for support material. Some support materials could be recycled, so this becomes less of an issue there. Also, imagine rendering a tube on its side. Now support the upper arch while it's being printed.
For vacuum-forming...makes sense, but you're talking a LOT of little pins. Personally, I think I'd just make a porous master on the rep-rap, (in sections,) possibly lubricate it, and lay it on the vacuum former.
Please remember, I've yet to handle a rep-rap, and I've never used a vacuum former. Weight all my comments accordingly.