I'm new to these forums but I am very glad I came across them. I am 21 years old and I have started my family, now it's time for my career. I have some college education and am about to go to ATP flight school full time. When I'm done I will have 1500 hrs and will be able to fly as an instructor, however I have a few questions.

Does size matter?
-I have gone to two instructors and noticed I could eat both of them together for lunch. the second one I went up to looked up at me and asked "You are a little big to be a pilot aren't you?". I told him "Hey, Goose was a big guy!" I am 6'2" and weigh about 220 (I'm not fat so there's not a whole lot of weight to be lost). Would this be an issue to certain employers? (I want to fly cargo, no people)

Just how hard is it?
My honest to god dream gig is flying for FedEx but everyone I talk about it preaches doom and gloom about how difficult it is. Are there any tips about what I can do now to better my chances?

Thank you everyone and I look forward to your responses.