I have/do ride long day rides when I can.(450-600 miles preferably alone on long trips)
That is for a different thread as to why.
Since you don't know how you are going to "feel" om this bike,I would not concern myself with mileage numbers concerning distance traveled.
If you set in your mind,"I need to go 120 miles between stops" for instance,you will fixate on this.
Depending on your mindset this can cause stress and anxiety.
Stress/anxiety causes fatigue.
Each time you travel that distance under stress it gets harder and harder when you are not feeling perfect.
Here is what I do:
Eat and drink something,clear my bladder as much as possible before I leave.
Let my body/mind dictate the distance.
If I have traveled 75 miles and keep thinking I need to stop,I do.
If I feel like going 200 miles,I do that also.
Unless it is for a "main meal" stop,I limit the stop to 15 minutes.
Eat a snack,use the bathroom and most importantly..stretch.
Try to stay away from sugary snacks as they will quickly wear off and cause drowsiness.
I carry "Pure Protein" bars that I buy at Walmart.
Relax and enjoy the ride.
This may not be what others suggest.
It is just what I do.