Get the Infotainment Upgrade. If you are OK with spending the $2500, it's possibly the best upgrade you can get even with an AP2 to HW3 car.
#1 - No new cameras or radar is needed when they do your AP2 to HW3 upgrade. You get everything that AP2.5 5o HW3 get except for the new visualizations. You now also get Sentry Mode and Dash Cam. If you get the Infotainment Upgrade, you also get the built-in Sentry Mode and DashCam viewer now.
#2 - There should be NO labor charge. Everything is part of the $2500 + tax. Print this out and show them the information where it says $2500.
Infotainment Upgrade
#3 - Yes you can use the USB Thumb Drive, but I found that a SSD hard drive is even better. I went with the one from
TeslaCam SSD Extreme - Pure Tesla
#4 - You will find that once you do the Infotainment Upgrade, you will get a new LTE modem, and Wifi modem. LTE connection improve a lot and don't worry it still have 3G support for when there is no LTE coverage. With wifi, you now get 5.0 ghz support so even faster downloads over wifi.
#5 - There really isn't any check-list per say. I would recommend you get very details photos of your trim around both your Instrument Cluster, and your MCU and glovebox. They do have to split open things to get the old IC and MCU out, and remove your glovebox to replace your AP3. And by detail photos, make sure to get all of your silver trim around your dash, from the drive side and all the way to the passenger side. Also make sure to let the service center know that the new IC screen has a plastic film on the display and they should remove it before installing the new IC. There are a few posts here where they didn't remove it.
I did the Infotainment Upgrade on my 2017 Model S back in March and it was the best possible $2500 to spend. Well worth it. The wife's Model X we just got the HW3 upgrade, as our VIN is not yet up for the Infotainment Upgrade just yet.
Here is my original writeup for the Infotainment Upgrade =
Tesla confirms infotainment system upgradeability from MCU1 to MCU2 for $2500
Note: On my original 2016 Model S which had the original non upgraded audio system, I did the aftermarket NVX sub and a speaker replacement in the door. The installer just tapped into the existing amp which was at the time located near my left knee, so far away from any MCU, IC or HW3. Just sharing that experience in case yours may be in the same spot.