Good luck with your project. I think that as a business school type project its certainly interesting enough and will probably cover all the basis to allow you to present a solid academic piece of work. Unfortunately I do however tend to agree with the other posts above that you are intending to enter a market that is pretty much already saturated with devices and it will be hard to make yours stand out from the crowd.
Virtually all the features you highlight are already available for free (or virtually free) on phone apps or come as standard with bespoke sports watches that offer additional features as well.
For interest how have you priced your footpod? (Garmin sell one for £30/40 so asume the actual price is a fraction of that but doing the whole thing for less than £15?
In answer to your questions
1) No I use a Garmin. I dont want to carry my relatively expensive phone with me when running and risk damage/loss to it.
2) The challenge here for you will be getting scale /take up to make it relevant. On sites like FB there are dedicated runners groups where people post this sort of stuff with hundreds or thousands of contributors. Then there is RW or Fetch or several others let alone the bespoke sites from garmin etc. I personally dont want to chat on another device specific website.
3) There may be something in this one especially for newer "fitness" driven runners. may be worth exploring more if the app could be more of a general fitness app but that market space is quite crowded as well
4)Not that I can think of
5)I think your target market is unlikely to be experienced runners who already will have access to many / all of the features. There may be a market for newer fitness driven people who like the complete package approach and want something more than a simple app (so adding the footpod if it really does add something - does it?) but arent willing to invest in a Garmin etc?
Its doable just in my opinion not a great idea for your first (and second). There is nothing magic about multiple marathons and many people do them week in week out - but generally they build up to them over time.
As well as fatigue I think you risk in some ways underplaying the great sense of achievment of finishing your first marathon by knowing you have to do it all again in a few weeks time. Many people find the experience of their first marathon a physically and mentally draining experience and take a month or more off running completely afterwards as they simply cant face it after the long hard slog of 16 weeks training and then the event.
If you dont want to let the charity down why not just do London for teh Charity - its the race that you will get maximum attention for from your non running mates anayway.