My old commute was 8.8 miles, with most of it along a MUP. Current one is only 3.5 miles on streets. The longer distance was a challenge at the time for my fitness level, yet I enjoyed it more.

As has been suggested, load up with what you'd consider you need and try it on a off day. Having done that, and doesn't appear that it's too difficult, then (if at all possible) drive to work on like a Thursday, ride the bike home at the end of that shift. Then ride bike into work and drive home. Off days are nice to make exploratory runs, but sometimes the traffic patterns differ on those days as well, which can have an impact on your timing or confidence levels.