Hello Kiley Freshwater,
You have many great resources already mentioned.
Yes, you want to combine all the training methods you mention. Cross training is beneficial. I would prefer the mode you will be using in the marathon to better prepare you; weather permitting, of course.
The bulk of your training will be in steady state cardio, with less training in the higher zone, so do some intervals when you feel ready.
Also incorporate strength training for the whole body twice a week.
I do not know if you will be biking and swimming with running. If so, you will want to do similar training for the bike and swim.
Make sure to eat, drink and rest properly as the others suggest, also.
Good luck with the marathon; enjoy every step.