Be disciplined with your breaks. It's amazing how easily even a quick stop to check the map can turn into a 15-minute stop, with people taking their jacket off, applying sun cream, eating a snack, checking their phone etc.
When estimating arrival times, forget the average speed that your milometer tells you. It's the average INCLUDING all the stops that counts, and for an unsupported team of four you will do well to go faster than 8mph, especially early on.
Make sure your brakes are in perfect working order before you start. Whatever route you take, you will need to do lots of braking!