I used the RW plan for my first marathon a few years ago, and just missed out on a sub 3:30 (but that wasn't the plan's fault). Just because the plans a few years old, doesn't mean its out of date as the fundamentals haven't changed in this period.
Since the fist attempt I've used Pfitzinger & Douglas upto 55 mile plan from their "Advanced Marathoning" book, which has been used by a lot of forumites.
The other option would be Hal Higdon plans that are widely used and recommended.
you will probably not find many people who have tried both, and most people will advocate the device they have. Have you read the dcrainmaker website as its the only gps watch review site that you need?
Its a bit difficult to guess as it comes down to the individual fit, but I wear 8.5 in the Mirage (versions 1 to 3). I also wore 8.5 in various Asics models in the past.
When you say "normal trainers" do you mean running shoes, or fashion shoes from a sports brand (e.g. Adidas Samba, Nike Air Max etc)? If its running shoes, you can use the shoefitr app available via the runningwarehouse.com web site (find the saucony mirage and click on the "show me how it fits" link). This will ask you what your current shoe is, and compare it to the Mirage. NB this uses american sizing, so you I think you would be a US 10 size.
You should be OK with the insole, the mirage has a bit of built-in support in the sole, so you could just replace the standard insole supplied with the shoe with your custom one,