Interstate vs non interstate miles depends a lot on where you are and where you're going.   Some trips interstates add a lot of miles for the time saved, some trips it doesn't add much miles at all and saves a lot of time.   Or in some cases a few more miles, about the same amount of time but much more relaxed driving than two lane roads with lots of stop signs and turns.

As for stops, if you get in a vehicle I'm driving and were going less than 4 or 5 hours, don't plan on stopping till we get there.    Empty your bladder before we leave and maybe think about limiting your coffee/soda/milk/water intake prior to leaving also.     

 I've made a lot of non stop trips to/from Des Moines over the years, that's a ~260 mile trip that takes a little under 4 hours.   Come home in the same day and that's a 500+ mile day, done that a lot over the years.

Thankfully HOS don't apply to personal vehicles but its probably coming and they'll have an easy way to enforce it with forced updates to Ed's Tesla while he's sleeping.      Reach your maximum hours and it just won't go anymore.   Of course many will applaud another govt mandate that removes freedom in the name of safety.