Bluetoe has written this in the past and the shorter first day or two is really good advice. Unless you will be able to get out regularly beforehand on your loaded bike close to or near the weight you will do your trip, for numerous good long rides (3, 4, 5 hours of riding) the first days are always going to be tough, there is just no way around this.

if you take anything from the opinions on the touring forum, this one of planning shorter first days is an important one.

All the best prepping for your trip idea.