Adobe Premiere Pro

Hello Premiere peeps! ok, I have some vhs 720x480 footage, digitized. when you dump that into timeline it matches settings automatically whichbis cool. but im using some 1080p footage too in the project. my 1st question is it best to drop in 1080p then add the 720 stuff and scale up? second question, id like to use 5.1 sound but it defaults to stereo when you drop in footage. if i manually choose the project settings, im worried i wont use the BEST settings for overall quality of project! any feedback is greatly appreciated! Billy