Hi Carissa! WOW...YOU GO GIRL!!! I am so happy for you that you have taken on this AMAZING challenge! Back in 2005 my husband, sister and I all ran the Marine Corp Marathon for the charity "Organization for Autistic Research" It was the most difficult thing I have EVER done in my life BUT it was also the most rewarding. The training can be arduous at times but know that you can vent/chat about it here and we will all keep encouraging you! You seem to have a very realistic approach which is KEY! I will share some things I wish I had done differently after I had time to reflect on the experience!
1. If you want to lose weight, I would try to lose as much as you can BEFORE you start your really long/hard training. Once you start that, your body will need more calories to replace what is being burned to prevent sickness/injury. While training, I lost only 4 pounds.
2. Do some strength training for your legs, they will take a beating when running. If you consistantly do some low weight high rep. leg work it will help tremendously, especially towards the end of the 1/2 marathon when you have depleted your energy...you will be STRONGER!
3. Sounds silly but once you really get into your training, practice drinking water or whatever energy replacement you will use during the race, during your training runs...it will limit your time that you have to stop and prevent cramping!
4. LISTEN to your body, remember this is a process, if you feel like you need more rest/recovery TAKE IT! This will go a long way to prevent injury too!
I am sorry if these tips seem scary, I just wish someone had thought to tell me these things before my race!
Good Luck, I'll be rooting for you!