Few comments FWIW:

Non-removable panniers are a poor idea. Your bike is going to be left outside, presumably, and without any way to bring your panniers into your tent, string them up into trees in 'Bear' country or put in a bear box you'll be relegated to un-packing them every night which is a PITA. If you think they may get stolen if they remove easily, bring a length of lightweight cable to lock up your bike and the panniers to it. I don't advocate heavy locks for touring since the bike likely won't be left out of site for long, cheap deterrent from casual thief's is typically all that is needed, pending location.

Chamois is the 'pad' of shorts, the cream goes on the chamois, or you, it's how its designed to work. Some can get away with undershorts, no cream, etc.....but it is an exception to the rule. Who cares what people think if you sporting 'cycling' clothes, being comfortable is key.

I leave arm-warmers at home and don't find them useful, I bring a wool sweater instead and use it for chilly mornings and around camp under my H2O proof jacket if needed.

I really despise bivvys after using one on a tour (my first) when it started raining. No place to relax, hide, drape clothes and get gear out of the weather. Also difficult to change clothes without getting everything wet. It was a major stressor and would never go back to one. With that said, try it first, maybe you have on your prior tour and it worked, some people can manage but on a long term tour I think comfort plays a very big role in enjoyment.