Hello again,
Speyer was "Freie Reichsstadt" from 1294 until 1792. So Speyer was subordinate directly to the Kaiser.
Don't mix Ros (short for Rose (english rose) with today's Ross or Roß (Pferd, english horse). And keep in mind that in 1599 there was no regulated spelling. In the context of this hymn the meaning is primary rose, no matter if written ros, ros', ross, roß, röslein (diminutive). The word Reis comes from Jesaja 11,1 and means Spross (english scion, but also sprout). One word, two meanings. I think, the meaning Reis is present in the background, when there is written Ros in the first line of the hymn.
Cheers
tiratutti