AKA L3X AV log'in prob's.
The answer to your first question is Yes.. The IS200 whether it's a NAV or NON NAv model will allow you to mute the headunit when the phone rings.. Simple one wire connection.
The answer to your second question is No... Not a straight plug in solution. The only one on offer from AUTOLEADS ltd is a Toyota plug in type to pass the phone audio via your IS200 Speaker system.. This does not mate onto the Amp output wire's... BUT can be modified to work, If you tag onto the speaker output stage of your amp ( located left side of the glove box).. Bearing in mind you will only need the front left and front right really. Autoleads Part number PC6-062
Yes, there are phone mounting cradles for sale. A basic one normally about £15, which is either metal or plastic.
You can get a full trimmed up leather one, from DASHMOUNT.COM i think, around £55 but looking very nice. FARGO has one.
The last question... I would say there probally is'nt a straight plug in solution offered by Lexus U.K for a blue tooth like solution offered on their high end LS model range. As I can remember the LS has a complete different system, with an additional control box, probally for the OEM blue tooth phone, and voice navi..