Help, engine sizes?

Before this gets flagged, please read because I can't find any solid advice here. I am 6'1, 230 LBS and I am gonna get my first motorcycle soon. My dad who is a touring bike guy, says I need to look for 500 minimum if I want to set out on the highway or main roads where 50-70 are the speed limits. Forums say 250-350 is where beginners need to start. I have no clue because I've never been on a bike. I am currently looking at a few bikes that are 500-650 but again, everyone says that's too much. Please help.(Edit - I'm not looking into sport bikes, I have no interest in them) via /r/motorcycles https://www.reddit.com/r/motorcycles/comments/edt5zg/help_engine_sizes/?utm_source=ifttt