So as you can see the TomTom is on the top mount, its got live traffic and speed cameras so makes driving much nicer especially as you don't have anything stuck on your windows. This would be a great location if you Phone, Phablet Or tablet doubles up as your navigation etc.
The Lower one is what I use for my phone along with a Scosche-Magnetic-Flush-Mount This holds my tablet or phone no problems
I am not happy how I have the power supply for the lower phone mount hooked up at the moment thinking of having it come out just below the air con controls, where the dash meets the gear surround.
The above mounts can get a little pricey as each Brodit mount is about 15- 20 GBP plus the adapter for what ever mount you want ie tom-tom or magnetic. So really your looking at 30 - 40 GBP in total for a solution. Its probably the best solution and if you spend long abouts of time in your car its well worth it! I drive 3 hours a day minimum and it makes the drives so much nicer!
Alternatively you can get one of these : Scosche Magnetic Dash Mount for Smartphone: Amazon.co.uk: Electronics
The downside is you must stick it to the car... and really in the 159 you can only stick it to the metal as the soft plastic is a bit too spongy and will leave a mark over time. My dad got one for his 166 and he is happy with it.
For the hardwire I would fuse tap the fusebox this means that your new power feed is fused and removable without cutting anything, now you can power what you want with a switched ignition.
I chose a 40W USB hub, you can power as many USB devices as you want and it registers an an AC wall charger so no slow charges with power hungry devices, I have charged my phone, tomtom, tablet and dash camera and still have a spare slot or 2.
Any question just ask