Re: Boxing Advise
Muscle = Power.
That's a myth. Tall lanky fighters not only have a great reach advantage but they also often get more leverage with punches than shorter guys. Height can be a gift.
Putting on weight will mean you're going to fight bigger guys where your height advantage will be reduced.
I'm not suggesting it's as simple as height = good, muscle = bad. But height is usually advantageous in lower weight classes.
I agree with Bazza, learn the basics, work on cardio, figure out your style and then decide what weight is the best. I promise you your outlook will change in a few months.
BTW - the hardest punch I ever took was from a 139 lb 6 foot 5 beanpole.