Stick to 15-inch or 16-inch wheels for reasonable ride comfort, then decide for yourself how much you want to spend. Leather adds to the status, but do you like sitting on leather? A built in satnav is nice, but a cheaper TomTom probably works better and takes UK seven-digit postcodes. A sunroof might be an option, although I actually prefer a glass roof so I get the rays without the noise and the dirt. The sound system is, again, up to you. Decent Bluetooth that works with an iPhone is essential, as are floormats, but the dealer should add them for free.