Add "sender/from" line to postal mailing labels
My solution for Question 1:

I create labels with the recipients in CiviCRM and save it. Than i create a label-sheet with the same format in libre-office only with the "from"-line and safe it as pdf. then i use "pdf chain" (for linux) to merge this two files together. in "pdf chain" it called "backround/stamp". so it "stamps the "from"-pdf as often as needed in to the pdf from CiviCRM.