Congratulations on your first marathon.

I've run 7 marathons and have never run any sooner than 5 days after a marathon. After my last marathon in November, I took almost two weeks off from running. A marathon can really beat your body up, and the risks of injury if you start running again too soon really outweigh the marginal fitness benefits that you will get from an extra week or two of running training. So, just start to swim and spin easily now and then get back to running slowly.

I think that running three days a week is a very good plan unless you are really trying to focus on improving your running. I hardly ever run two days in a row unless I am training for a marathon, and getting the day's rest between runs has really reduced the overuse type problems that I used to have.