3.0 base brakes are slightly smaller -- you need a different pad.
These are the size of rears you want: Endless MX72 Street Circuit Semi-Metallic Compound Brake Pads - Rear | Brake Pads for Toyota Supra A90 | TOP END Motorsports
I'd personally say you'll get the most out of a 911 by pushing it on a track, and that's where you'll experience the massive differences from an FR layout.
Drove a 991 GT3 in Vegas a couple of years ago, and it was extremely thrilling but also had a large learning curve since the car had much...
PSS and PS4S will get you about 2-3 sessions before they get greasy from my time on the track. Wider tires did offer a bit less tail happiness along with my alignment and corner balancing. I would go for track tires if the Supra was mainly a weekend and track toy -- they would get me a few more...
You may rub a little. I've got the 265-295 setup and there's basically no gap on full lock when stopped (I'm also lowered on coilovers with an alignment, so there's that). I've felt rubbing on rare occasion. I think a 275 will rub depending on your suspension geometry.
JB4 is the cheaper option for more power. For tracking purposes, there's a lot you can invest in with regards to handling for better lap times before you even need to consider more power.
I'm not sure its that simple. The platform is meant to be modular, and I highly doubt they use the exact same modules for the Supra and Z4 as they do for the X7.
A lousy wrap job will reduce your car's value, especially if it strips paint on removal. Also, if its not a standard color, some people may treat it as a mod and consider it as "non-factory".
A good wrap job can maintain the paint quality years down the line, but PPF is still better (I believe...
I unfortunately don't remember what size screw extractor I used.
And yes, I did run it for a week with just one screw. I didn't have any issues. I was also worried it might pop out or something and put the car into limp mode, but it didn't do that at all.