Hey!!! Congrats!
Just wanted to give you some more in-sight on how the drivetrain works. I also have a NIRO PHEV! In the past Ive owned Nissan Leaf's, Prius' and a Chevy Volt, this is my first plug-in hybrid. Its much different than Full Electric or Extended Range Electric (EREV) cars...ie the Chevy Volt.
The Niro PHEV has the ability to plug in and extend non-emission range/EV range. This varies on temp, driving style and conditions like elevation and weather. If you drive conservatively, no hard accelerations, you can stay in EV mode. Making your ECO needle go to POWER will kick the engine on. Additionally, running the heater will start the engine just to run the heater, not power the vehicle. So in the winter you can still get your 20-26miles of EV mode but will burn a small amount of fuel if using the heater.
Another benefit of a Plug-In hybrid, is you DONT have to charge the car...if you don't want, like cross country trips or weather is just to unbearable to go out and plug the car in. You will still benefit from the 40-46mpg running the car as a normal hybrid.
As far as the EV/HEV mode buttons, you can conserve some battery (say your fully charged and going on a long trip and just want to run gas) click the HEV button and you will maintain the battery state for the duration of your trip, the car will drive like a Hybrid. Sport mode will be FUN. I use it around the hills here in Northern California, gives me an extra boost when I don't feel like pounding on the gas pedal to get moving. There is a small hit to fuel economy, but play with it, its fun. Take the Transmission selector and pull it to the drivers side and the dash will change from GREEN to Orange and youll see a S. (also you can manually tap shift gears in sport mode as well)
Charging the car. this is a big one, The L1 EVSE (electric vehicle supply equipment), some people call it a charger, the charger is actually on the car, this is just your power cable. Its rated at 12Amp and 110v. Takes around 7.5 hours to charge the car. If you want a higher powered EVSE, a Level2 (L2) runs at 220v (dryer plug outlet) you can use any L2 EVSE. The cars onboard charger limits you to use 16amp at 220v, what does that mean? its 3.3kw max power. using a public L2 EVSE is generally at 30-40amps (6.6-7.2kw) but wont charge the NIRO faster than 3.3kw. You can pick up a L2 EVSE for cheap! I mean around $200. DUOSIDA is a brand which will charge the NIRO PHEV in 2.5 hours and all it needs is a 20amp 220v circuit in your house. Very inexpensive and quick to install. No need to pay hundreds of bucks on an expensive EVSE, no benefit unless your future proofing for a TESLA or another EV in the house/future.
The battery is located in the trunk space below the floor mat, there is no active battery management for cooling or heating, so no coolant to worry about, but the car does have a small fan on the battery to blow heat off of it. You might hear it on warm days if the car was sitting in direct sunlight. (I have not heard mine)
I could go on forever, let me know if you want more info.