My 5th gen was under-filled whenever I changed my transmission fluid change w/filter. It was slipping a little bit; was about almost a quart short. I hope it's not like this on the 6th gens. I believe there's a video of a 4th gen Tacoma on YT somewhere who did his transmission fluid change.
I installed it a couple months ago, mainly because when I did crack the rear window down, I could smell some of the fumes coming into the cabin and I hated how the stock muffler hung. With the SXTH Element trail pipe, I don't smell it at all and you only notice the sound a lower RPMs or at cold...
I currently have Ridge Grapplers, they're decent. They are getting louder as I have almost 15k miles on them. They don't perform well in the rain compared to the Wildpeak AT4Ws I had on my 5th gen. I'll most likely switch to AT4Ws after these wear out.
Installed my trail pipe a couple weeks ago. The sound is very subtle like you said. Barely hear the difference inside the cabin and outside, just slightly at cold start and low RPMs.
Yes, you can. Your friend would have to get an AI box then plug it into the port the normally takes Carplay/Android Auto. Also you would need to tether internet from your phone to that AI box.