Hi Andrew, glad to hear that you're enjoying your car.
1) I could do with a holder too. I've seen versions that replace the grab handle but haven't sourced anything yet, I tuck my case in the glove box for now.
2) I had a look at my clock setting and within the Info button I see an Adjust Clock option top right. However mine doesn't give an option to change the display between 12/24hr. I can't see the option in the manual either, online copies here; https://carmanuals2.com/brand/lexus/gs450h-2008-1890
4) Individual TPMS can be around £100 each but Richard recently found a garage in Leicester that would supply/fit them for around half that price. So you can hunt around for a more cost effective set. Sensors are coded to the vehicle, so when you swap to your winter set you'll need to reprogram the car to read these sensors. Some folks remove them from the tyres completely, pop the sensors in a pressured box and keep it in the boot - which stops the warning light on the dash. FYI: TPMS errors aren't an MOT failure for an '08 car.
7) beware the OEM maps come several different disks which I didn't like as travelling on the continent would have been fiddly. This may not be an issue if you only intend to drive in Blighty.
Cheers, Lee