We tend to plan around 'must' events and annual doctor appointments. Father's birthday, granddaughter's wedding, another granddaughter's high school graduation. Then fit our volunteer positions and desires into the balance.
Also try to not tow over 300 miles per day, and try to never tow on back to back days.
Reservations - only when necessary - One exception - Memorial Day weekend, Fourth of July, Labor Day weekend, Thanksgiving weekend, the week after Christmas Day through New Years - if we are going to be anywhere that might be a big family draw - we reserve a couple months in advance. Those are very busy times at good campgrounds. We don't want to be locked out of our desired area/ campground.
I work out a route on Microsoft Streets & Trips far in advance, but for actual travel - that is a plan, not a requirement. We may go off plan for a week, or weeks, skip stops, add stops, etc. The goal is to put enough flexibility into the plan so that we can make changes. And to be able to tell quickly at a glance how deciding to make a detour for several days might impact our need to be somewhere in two months.