Other peoples opinion may differ, but personally I don't think you should return to running until you can run with a completely normal gait.
I don't know what you're running style is like doing 2 miles in 25 mins, but try and be completely honest with yourself - if you're overcompensating with the other leg in any way then return to physio related exercise. Running with an abnormal gait could exacerbate the problem and possibly cause other issues. Above all take guidance from your physio/doctor, have they OK'd your running?
In my opinion this depends on your expectations. You didn't mention what time you did for your half so it's not clear what your base level of fitness was.
Noone is going to tell you that 4 weeks off doesn't matter, but it's more than possible for you to go from here and train to get around london, you'll just have to adjust your finishing time expectations. Just relax and try and enjoy the training and the race, there's always other marathons in the future.
My personal recommendation if the foot problems continue is to try another brand of shoe.
the ham muscles are connected to the knee through tendons which are directly behind the knee, so if you have pain in that area it's most likely going to be the tendons. Quite often though the damage is localised so you may have damaged both the tendon and muscle. Look up the symptoms of both tendon and muscle damage and see if you can identify with either/both.
Either way though you can't go wrong with RICE, the recovery time depends upon the categorisation of the injury. For cat 1 it could be 1 - 2 weeks, or cat 2 up to 4 - 6 weeks, it doesn't sound like it's any more severe than this.
Take your time, take it easy getting back into it and don't just go straight out and run, do some area specific strengthening first (again build this up slowly).
it was my first worksop half and i really enjoyed it. I did think it was a tough route though and the wind was pretty strong, i got back and checked the weather and the bbc said 45kmh! The straight leaving clumber park at about 18.5k was really tough going into the wind.
I managed to pb by a few seconds but i think i can safely say that's down to my training!