I think all of your questions depend on what type of turning you are going to do. Sliding and swiveling headstocks are great, and a compromise in price/function, but each have their weakness in the struckture. Sliding headstocks will often "jack" or slide as you push the tailstock in further against the wood. Rotating headstocks will not have as much structural strength in that it is at a different angle to the bed (my personal opinion, I am not an engineer). If you anticipate doing even occasional large work (say greater than 24"), I would look at a purpose built lathe or one that has the heft to do the outboard capabilities for it. Personally I use a Oneway 2436 with standard capacity of 24" and outboard capabilites to 48" and it can be real harrowing to deal with something that big rotating that close to you. I think that even their outboard attachment isn't large/wide enough to adequately accomdate it's potential capacity.
As far as the pattern makers lathes that didn't have a bed, the ones I have seen did, it was just a very heavy steel plate setup that was the floor you stood on. They had dovetailed floors that allowed alignment of the pieces as they slid.
I found one a few years back, reasonably priced. Had about 60+" swing, but weighed 3000 pounds was 7'x14' of floor space and was in Rhode Island. I figured it would cost as much to ship as it did to buy.