My day-to-day flat kit includes a spare tube, tire levers, patch kit, tire boot, mini pump, CO2 inflator, and Grease Monkey wipes. I also carry a bike mini-tool that includes the 5mm hex I need to remove the wheel through axles though it looks like your model has 5mm QRs.
I always carry a water bottle and have cages for 3.
For longer rides, esp on gravel, I add a 1st aid kit.
For out of the area trips I add a travel kit with a chain master link, pressure gauge, etc.
As to tires, there have been several posts praising the Schwalbe Hurricane as a good all-around tire. I went with the Schwalbe Marathon GT Tour for a bit better puncture protection. I also put tire liners/thorn strips in them. Nothing's puncture-proof, but it doesn't hurt to try.
As to the chain, your mid-drive bike does put more stress on the chain so it needs more attention. I give mine a wipe down with WD40 after every gravel ride with a bit more lube and clean and lube it every few hundred miles. The likelihood of breaking the chain is fairly small though a spare master link and a min-tool with a chain tool don't take much room. The real risk is letting the chain wear too much thus damaging other more expensive (and right now harder to get) drive components. Wear gauges are handy, but not a great predictor of when to change an ebike chain. Others have reported drive component damage when the chain mileage got in the 2,000+ mile range. I change mine every 1,000 miles or so just because the chains are a lot cheaper and easier to get than the other drive train components. By my standard, you're ready for a chain replacement but my ebike has more torque than yours and I ride in a very hilly area so even more chain wear. Your call.
