To be honest I'm not really one for buying used gear if I can help it, I am seriously thinking of this http://www.ebay.co.uk/itm/182253604089 it's USB, 800w water cooled spindle & has ball screws, but I'd be hoping if I bought this I wouldn't have to spending much on it for a while!
Font size I haven't even thought of that yet but I would be thinking of probably about 8-10mm high on these stencil type things!