For starters, congratulations on setting a huge goal for yourself!! In my experience it's setting goals like that and getting registered for races that turn wishes into reality.

As far as the treadmill training, if you absolutely can't train outside there are various programs on most treadmills to help combat stagnant training. The random setting for most treadmills will alter the incline at various percentages for 30 seconds to a minute. The downside to the random setting is that it's counter intuitive to the Smart pacing strategy that I adhere to. (and to that end I cannot recommend Smart Pacing or Pacers in general for distance races, it will help you accomplish your goals and have fun while doing it!)
Smart Pacing is a mutli-faceted strategy that takes into account that every race and every mile is different. It takes into account inclines, declines and fade. In other words, unlike a treadmill, you will not be staying at the exact same pace every second of every mile of your race. You'll want to start out conservatively, take inclines easy, downhills are free, and finish strong. Back to the treadmill, using the random setting you'll want to increase your mileage by about 10% every week minimum. You'll also want to be running at least 4 days a week but not more than 5 (rest days are important to prevent injury as you build your mileage).

But, I would strongly recommend checking with local runners (maybe find a running group, running specialty store, etc) and check with them about safe routes or other areas you can run outdoors or on a track. I live in a small town in Kansas with a particularly high crime rate that's not pedestrian or runner friendly at all. But I still have 3 walking/biking/running paths that are at least a mile in length and well lit. So they exist pretty much everywhere, if you time things right you should still be able to get in outdoor runs.

Even if you can't run outdoors until after August that still gives you September and October to get back into the swing of outdoor training. If you've built your mileage up and done appropriate interval and incline training on the treadmill, you should have minimal setbacks in your transition outside. The most difficult part will be learning to pace yourself again.

On to food. My favorite topic lol. Pre-run and pre-race I stick with whole grains and water. But I won't eat or drink anything substantial in the hour leading up to my run. Some runners like myself experience horrible heartburn while running so I have to take a daily preventative antacid and right before races I take malox in addition to that. So what I eat has a big impact on my run in all sorts of ways. Post run I always always always go for milk, protein and fresh fruit or veggies. They have pre-cooked chicken breasts you can buy frozen, those would be a great option, and steamable veggies in the frozen section. As long as you've got a mini-fridge/freezer, you'll be ok!! And find what works for you Everyone is different in their preferences. I know runners who absolutely can't eat right after a run, and others who insist on drinking a ton of water right before a run.

No matter what, make a plan for yourself and do your best to stick to it (accounting for bad run days, sick days, PMS days, etc). And KNOW that no matter what happens you WILL cross that finish line. No matter what your pace, no matter what it takes to do it, it will happen. And it will be an incredible accomplishment!! Keep up the great work!

I think cross-training on rest days is good, I like to mix it up and combine strength training with my runs or hopping on the eliptical when I'm prepping for a big run the next day. The big thing is not to overdo it and to give yourself at least 1 full day off of everything per week. Rest days are just as vital to your training as anything else, overtraining can cause permanent damage and really set you back from your goals. Swimming is a great low impact activity and it burns crazy calories! It also takes a lot out of you for that reason so be sure not to do that within 1-2 days of any big runs your planning. Your body just won't have the stamina it needs.

Good luck and stay positive!!! Keep us posted on your progress!