Sounds like a fun trip. People must think we are crazy to talk about riding such distances. I know I used to.
You are asking one of those "religious" questions where logic and reason will soon be swamped by dogma and faith. I would suggest you try it for several days and see what you think. Have you weighed the rig, loaded, with you on it?
(1) Find a bathroom scale and a block of wood the same height as the scale.
(2) Weigh yourself, your bike, and your gear to get the total weight.
(3) Load the bike down, put one wheel on the scale and the other on the block of wood.
(4) Manage to stay up - maybe lightly leaning to a wall or someone holding you, have another person read the weight.
(5) The weight in #4 / #2 gives you the percentage weight of the wheel over the scale.
Having said all that, I usually tour with four panniers. And, lately, I have been training with only weight in the rear panniers. The rides and handling are very different. I suggest you try both, for some extended rides, on flat ground, climbing, and descending, before you decide.
But the most important thing is that you decide. Do what feels comfortable and works for you. After all, you are the one that will be pedaling down the road, having a grand adventure, not us arm-chair riders.