Endurance Running While Losing Weight?

i think its trial and error with running. You can definitely build up fitness and endurance while losing weight, but you probably wont be getting your best times etc, and i would try and put your deficit to maybe half a pound a week at first and then if you feel good on it, try 1lb a week.
i think 1300 net is fine, but its all about how you feel on it.
I definitely run better when my deficit isnt too high

Yes you are likely to lose muscle mass from endurance exercise. I am actually doing that on purpose now, because after much research I had learnt the best way to lose muscle off my thighs was to do long runs. Also, I am sticking to 1200 calories a day and have found that it is getting harder and harder to run because I just don't think I'm fueling my body enough. I agree with comment above about focusing on the half marathon and giving your body enough fuel in order to achieve it!
I think you will find you will probably just lose the weight quite naturally by training for a marathon anyway.

My experience is that yes you can train and race hard and loose.
It is important to fuel correctly before, during and after training.
Aim at a small loss, (half kilo per week or less) and be prepared to eat a bit more than target if you need, especially on big training days.
A week before race I would not have a deficit and definetelly eat pleanty on the day before a race and a couple of day after.

Run specific weight training and general weight training whould ensure you retain lean body mass and help performance too.

I use early season run programme and half marathons to get in shape (loose weight too) for the summer season main races every year, so it is not a great loss of weight (max 5 kilos depending some year more, some less) but the aim is to loose body fat for main races. So I for all I know it is possible and it can work well, just try to tune in with your body requirements to acheive both goals.

Good luck!