The idle crickets are the HP fuel pump, Toyota did a warranty job on them but most of the crickets came back! To comply with Toyota recommendations, use only 98 Ron petrol,Shell V-Power or Tesco
I believe the crickets are to do with the amount of ethanol in the fuel. I get the crickets when using Shell V-Power and Tesco Momentum 99. But I don't when I've used Esso Supreme 97 - which I believe is the only ethanol free petrol available in the UK.
But to the OP.....don't worry about it. It's a bit annoying, but it doesn't do any harm. I've had the crickets since day one in my 2013. Apparently they revised the high pressure fuel pump in later models, but I don't know how costly or difficult it would be to change.
As for the other issues:
- Brake judder is probably just a build up of pad material on the discs. Take the car out, get the brakes warm with some fast braking, then do some repeated hard braking from high speed, but don't actually come to a complete stop. Should clean up the discs nicely. If you've still got issue after that then look at maybe replacing pads or discs, or investigating the slider pins on the calipers in case they are binding a little.
- Diff: not sure, but a good start is to the change the diff oil. Easy to do yourself, and cheap. And as growlerkat says, it's a regular service item.
- Gear knob: if you cant fix it with glue, I'd just look for a replacement gear knob personally. Mind feels a little loose sometimes, but hasn't come unstuck.
- Rear view delamination is a common issue with the frameless mirror. I go my first one replaced under warranty after a few years, and then just recently the replacement started doing the same. You can buy frameless replacements on eBay, but I just replaced mine with a mirror from a Subaru WRX (I think?). Cheaper, and it has a frame, but at least you wont need to replace it every three years.
- Headlight haze: I have this one only one of my headlights. Drivers side light has a slight haze which I've cleared with some bodywork polish, but it's still there. Some others on here suggested Meguiars Plast-X which I'm going to try next. Passneger side light is crystal clear though.
- Seats: cant help you here, other than to say my driver's bolster is pretty worn, but then I'm a fat git. However the seats are otherwise in good condition.