Basically, eh, no mate. 1 mile the matter how many times you do it isn't really far enough. You need to be running a minimum of 3 miles in a go, as that's how long the run is on the PRMC.
I'd say run 4 times a week. 2 x 3-milers, 1 x 4-miler and 1 x 5-miler. Also go cycling on another 2 days and have 1 day off. Your circuits should cover you for the press-ups, sit-ups and pull-ups you'll need to do.
(you might find this too hard to do, so just work up to it and hopefully you'll be doing that much in the last weeks up to your PRMC)
Yes, basically you should start at 1 mile to prevent injury. The rule of thumb is to increase distance by 10% each week but you'd be there forever so after 1 maybe 2 weeks go to 2 miles, another 2 weeks 3 miles another 2 weeks 4 miles and advisably end up at 5 miles (to immitate the PRMC 3 mile run). Don't go balls out fanny flapping because it'll never work and you'll just injure yourself and set yourself further back.
Remember 10 runs at 1 mile, 10 runs at 2 mile, 10 runs at 3 mile, 10 runs at 4 mile, then hit the 5 milers and stay between doing 3 and 5 milers untill PRMC. A few hill sprint, intervale session and maybe a few long distance (half marathon or something) should keep you ticking over.