Yes, people use computers. If you're comfortable with, and already within the Garmin ecosystem, I'd look at an Edge 530 or the 830, which is very similar to the 530 but adds a touchscreen.

Your power meter likely broadcasts in both ANT+ and BT - it'll be compatible with the above computers.

My tubeless flat kit is the same as my tubed flat kit, I just don't have to use it nearly as often: spare tube, a couple patches, a pump (some prefer CO2), and tire lever. The only additions are a few plugs ("bacon strips" in my case) and a tool to insert them.

I can't think of any reasons to stick within Giant accessories except for anything that'll go over the steerer tube, like a new stem or possibly a computer mount; Giant uses an oversized steerer that's larger than the industry standard.