As above - save your money and have a go yourself, it is a very straightforward job. Headunit and speaker choice will be down to your budget, obviously you can spend quite a bit
wash and dry followed by taking all the lights and spoiler off the hatch to clean with brush as previous owner/ s had stored it by a tree and all green gunk was surrounding the light clusters and in behind spoiler - time well spent
my 2008 hatch has a space saver wheel. PCD is 5x100, the offset I believe is 55 but stand to be corrected on that one
Just checked tyre details on spare - T125 70D17 98M
This link gives more info on Subaru wheel sizes
http://www.cars101.com/subaru/tiresandwheels.html