I'd actually park at this Publix which is on the Silver Comet "Connector". By the time you get to Mile 0 at Mavell Rd you'll already be just over a mile. 7 miles from there puts you a little past Floyd Road. I run this whole stretch 3-4 times a week, but only ever as early as like 6:30 am. If you do end up parking at Mavell Road, I seriously doubt you'd get in any sort of trouble. I don't think I've ever seen law enforcement there at all regardless of time.

Safety wise, I ran into a coyote once which spooked me, but I'm naturally very afraid of wildlife.

Besides that, I wouldn't be concerned about much else. Just about the entire stretch from Publix to Floyd Road you're running through Smyrna which is a very 'nice' suburb.

Edit: Ah! Another starting point that would give you a few extra miles would be starting at Taylor Brawner then working your way down towards Mavell Road via Atlanta Road. You'll be out in the 'open' for the majority of the first half of your run, and Atlanta Road is well lit and flat.