I bought a Viofo A139 Pro about 4 months ago when they were initially released and I love it. It is my first dashcam and I have it in my 2022 Subaru WRX and opted to hardwire it with a BBMC Powercell 8. As you can tell, I'm not an expert here but will attempt to answer some of your questions:
Best firmware to upgrade it too?
I'm running the latest publicly available version off of their website of V1.0_1217. This sounds like it may be updated soon by Viofo and I'll upgrade when it is.
Can I get the best recommended settings and the largest and best Micro SD card I can buy
I run a SanDisk Max Endurance 256GB card in mine and have the Viofo 128GB card that came with the unit as backup. Per the manual, 256GB is the maximum recommended by Viofo, however I have seen others running higher. Here is a link to recommended cards:
What memory card is recommended for a VIOFO dashcam?
For general settings I have my resolution set to 4K 2160P 30fps. I leave my HDR set to on. Not sure if these are the best settings, but it is what I run with.
As to other settings, some of these may be fairly subjective on a case by case basis for what you want to accomplish. For instance, I have clear window tint on the inside of my windshield for IR/heat rejection. If I use the included CPL in the daytime, I get a horrendous rainbow effect, so I do not use the CPL at all. For my rear tinted window I have the exposure value @ +1.0 which helps with my tint. Other options like Loop Recording time, Audio On/Off, Parking Recording options are very subjective.
Any tips for installation I should be aware of?
This was my first dashcam/battery installation and I choose to do it myself and to do it with an external battery for parking recording. Not the least complicated route, but overall it wasn't hard to do. It greatly depends on how you want to run the unit (by using the provided 12v plug or hardwire to a fuse tap etc.). The most time consuming part I found was hiding all of the cable in the headliner, weather-stripping, pillars, etc. There are a lot of good videos out there for accomplishing these things and probably one out there that someone has done for your make/model of automobile. I'd research like I did to make your installation easier.
Good luck and hope that you enjoy it! I absolutely love my A139 Pro and the best decision that I made was to spend the extra money and get the battery pack.