I have only run one marathon although I did run 47 miles the day my dad died (kind of a Forest Gump thing…I guess)
I only did a marathon just to say I did it…and it was tough for me, because typically as a sprinter I trained at shorter distance between 5-8 miles, 6 days a week.
Marathons are hard on your body and diet is very critical. Go online for “distance running” to figure out your desired nutrient intake ….there are also formulas for the amount of carb intake according to your weight.
As for training, I did 3 – 20’s prior to the marathon which I scheduled so as to have a 3 weeks recovery before the marathon…. although I did maintain my 5 daily miles throughout (with a 2 day break after my 20’s) But ….you should do what you determine is best for you.
Weights are good... bike and elliptical are different….You are using different muscles with each as opposed to running ….especially on a bike…I would go with elliptical and treadmill ....that would be my choice…but again …..you determine what is best for you.
Stay safe