hello mate, and welcome.

Im other end of the scale so maybe we can help each other.
Last year i was 6'1" and 10 stone, but a year on ive managed to get to 13stone, and do look quite well toned. I do really wanna get to 14 but cnt seem to get there! i hava massive metabolism, meaning i can eat 5meals a day (1 being a meal replacement shake) I really want to add some size to my arms, any advice?

In response to your questions, its never to soon to start running/jogging, just make sure to warm up n down properly else you'll get serious aches (especially at you size) and start small, like a mile jog every 2 days. Also try cycling as its less impact than running!
As far as being laughed at at your gym is concerned, if u get laughed at its not a very good gym. No matter how big people are that come to our gym, if you want to learn and give ur all then people are always willing to help!
As far as supplements go, steer clear of creatine for the moment, and do more cardio than anything - you want to be burning more than your eating for a few weeks. Other than that, itll just take time and commitment.

Hope ive helped and not rabbled on!