Hello Brian,
10 miles as a longest run will get you through the half marathon- if it was me I would probably go for slightly longer runs in the next three weeks rather than upping the pace as its going to be endurance/sustained running that will benefit you more. You'll need to taper down the training as you get towards the event as you don't want to get to the start line exhausted or overtrained.
For the weight loss, I'd personally aim for about a 500 calorie a day deficit- which equates to 3,500 cals per week and about 1 pound loss per week. Training on starvation rations is no fun and the speed increase from the half stone reduction although noticeable will not be huge.
Good luck in the half and do let us know how you get on.