Geoff, "hose," whose plural was "hosen," varied in all those particulars. There were joined and unjoined, footed and footless, etc. Usually they did have feet, and sometimes the feet had leather soles so that shoes were unnecessary. (This makes the rhyme I quoted above charmingly symmetrical; "hooded and hatted" and "hosed and shod" both show Robin with a "belt-and-braces" approach to dressing!) Many times they were joined in the back but not in the front, which is where the codpiece came in, to cover the gap in front. It's hard to picture what Robin should look like, because we don't know what era to picture; the ballads are all late fifteenth century or later, but if there was a "real" man he was probably around two hundred years before that.

The ballad writers were presumably thiking of their own era's fashions when they wrote. This would likely be a pair of hose, either separate or joined in the back, worn over braies or linen drawers on the bottom, and tunic or a "gown" over a "shirt" (i.e. an undershirt) on top. Even if the hose were not joined in front, the middle-class tunic or gown would be long enough to cover the naughty bits, and there was an undergarment there as well!

To answer your other question, all ranks wore hose, but the cut and quality varied greatly, more or less like "trousers" in our day. Think of Brueghel the elder's paintings, for example, which show sixteenth-century peasants in hose (which look essentially like tights). Brueghel's upper garments are often long enough to "cover," and sometimes short enough to require a codpiece, but he was a hundred years later than the early ballads and hemlines went up in that time! So the fact that Robin is wearing hose says nothing about his social state, it's the quality of the hose that would be telling!