Crossing the USA from Tampa, FL to Western USA and back

Mark the start point. Mark the furthest point. Start adding waypoints/attractions. Click the calculate route button on whatever software being used & see what you have. Insert how many days where for each stop & calculate again. Take a guesstimate on how many miles you are happy with per day for between stops, insert & calculate again for time needed.

Subtract or add destinations to suit time available & calculate again. Spend months tweaking & researching. Be prepared to change anything on the fly.