I am assuming this is for an extended (several weeks) bike tour where you expect to rarely have an opportunity to plug things into an outlet.
I have found that when I have both my Sinewave being used to charge something and a light on, the Sinewave is putting out so little power that it is not worth doing it. You wire both the charger and light in a parallel circuit. When nothing is plugged into the SInewave, it draws almost no power. And when the light is turned off, it draws no power. So it is quite simple, you want to charge something, turn the light off. When you are not charging anything you can have the light on or off. In other words, I am disagreeing with the manufacturer.
That powerbank is rated at 100 watt hours. Most of the time the Sinewave would be putting out about 2.5 watts, 3 if you have a tailwind. Yes it can put out 5 watts, but that is down hills. So, to charge up that powerbank from being empty to full you are looking at around 40 hours.
The Nexus 9 tablet, I have no idea what the power draw on that is, my small (7 inch) Android tablet usually draws about 4 watts, thus if I took it on a trip I would probably need an hour and a half rolling time for every hour the tablet is on. In the past I only had it on when I had wifi since I only used it for weather forecasts and e-mail, so usually less than a half hour a day. If you use your tablet a lot of hours each day, you are going to run out of power.
A friend of mine has that taillight. He likes it. But if you are riding in front of someone and ask them to tell you if it works, warn them before you suddenly slam on the brakes.
IQ-XS does look like a nice light, I bought one for my rando bike, but waiting for spring before I can try it. Have not tried it yet.
A headlight that burns through 4 AAA batteries in 6 to 12 hours is using a lot of power. I bring battery powered taillights (two) on bike tours but I have not used a headlamp during the daytime while touring.
I have tried several different USB powered AA/AAA chargers, some are good and some are not, and several of the ones I have bought are no longer sold so those I am not going to suggest because they are hard to find.
This one works well when powered by using a charger plugged into the wall or from a power bank. But it works poorly when powered from a SInewave unless you are using a pass through cache battery. Since you are only charging from a powerbank, it should work well for you. It is a smart charger, meaning that it charges a battery faster than a dumb charger and will shut off when charged. And it has a separate charging circuit for each battery which is good. Also quite small and light weight.
https://www.amazon.com/Powertravelle.../dp/B00DQQLMCK
There are cheaper AA/AAA dumb chargers out there that are not very good, they charge very slow and keep charging forever.
AA and AAA batteries, I like the white Ikea Ladda best. (Ikea makes a cheaper brown one, avoid that.) A close second place is Eneloops. I have only used the white Eneloops, never tried the others.
https://www.ikea.com/us/en/catalog/products/90303880/
Amazon also sells them at a much higher price.
On your tour, bring a charger that you can plug into a wall too, there might be times when you have the opportunity.