Feedback request on training plan

I did some research and based on that put together a training plan for my wife and me to get ready for the 50k Cowtown in February.

Originally I had found a 50k plan online, but after further consideration I felt the weekly increases of more than 10% and lack of rest-week might increase the injury risk too much for us.

 

Some elements of the plan I found I took over:

- longest run 24 miles

- running 5days a week

- mileage peak at 57

- weekly mileage of the last 4weeks

 

Other key-elements for us are:

- Monday and Friday non running

- Wednesday 3 to 4 mile run (after swim in Loyd Park)

- Long run Sat/Sun (though I would consider the days interchangeable)

- 4week cycle (every 4th week is a rest week)

- 13.1 run on 2/3/12

- 3.1 run on 02/23/12

- Monday and Wednesday are swim days, possibly one weekend day

- Biking is not planned, might be sprinkled in as desired

 

About us:

- started running in June 2011 (back then we could not run 1mile)

- Finished 4 Half Marathons this year, some tris and other races

- both have BMI in normal range (normal weight)

 

My points of question:

- A factored a 20% drop in weekly mileage for the rest week, is that a good value?

- Is 24 for longest run truly sufficient?

- Is weekly mileage peak of 57 sufficient?

 

Goals are:

- Finish 50k in under 7hours

 

Any feedback is welcome!