Well done on joining the running fraternity! Although it will never replace playing rugby, not for me anyway. I was/still am 16 stone and have been able to complete several marathons etc. I run on a regular basis. The key for yourself is find a programme that has made 4 run sessions per week- My Asoka or runners world are good for this. That way you will not do too much too soon. Dont worry about the weight it will come off. Key is a good pair of trainers and a gait analysis.other days either weight train or rest. but the programmes will tell you that.
take it nice and slow and you will be amazed by the results. #good luck