I wouldn’t try any additives. The IS250 uses direct injection, so just make sure it’s had it’s maintenance done on time and you shouldn’t have to worry about carbon buildup.
The EX was the last of the model year range so it will have the best of the updates over the years (there were like 3 or...
A simple flat battery can cause all sorts of lights on the dashboard. Is the car driven daily or does it stand for days while you're working from home?
Warranty and maintenance plan yet they still asked you to arrange to have the vehicle towed in yourself? Does roadside assistance not cover this? Hope you did not pay the AA for the tow as your insurance would've done this for free