Hi There,
Firstly, I would personally recommend the IS300h, my parents drive this model and they get 50mpg+ mostly (dips to 48/49 with heated seats on etc)
My mother drives from Glasgow to Edinburgh (& back everyday) and this is about 100 miles a day, car is 2014 Premier model and it has never had a single issue. It has a service every 10,000 miles and only gets the brake pads or wheel alignment for.
We got our cars from Lexus Glasgow and they are fantastic through and through! Service from them is A+ and Lydia there is most helpful.
If you are buying non pre approved then make sure to get the hybrid battery checked.
With regards to warranty my family has never taken out a warranty on any of the past 3 Lexus cars they have bought so I would say you should be safe, but go for dealer for piece of mind if you want?
I have some video's on several Lexus cars if you want a more detailed look at them?
I hope I helped?
Feel free to ask any questions?
Thomas x
PS Merry Christmas