Well, I've never imagined Maglor to be chubby, but who is to say he wasn't? All I have ever heard about his physical description is that he has dark hair (probably in "The Shibboleth of Feanor"). The only Elf I know of in canon who is described has carrying a bit of excess weight is Salgant of Gondolin, I believe in The Book of Lost Tales II, "The Fall of Gondolin."

I think, with regard to his duties, a lot of people have differing opinions of Maglor - some consider him a warrior no less than his brothers (often reasoning that he killed Uldor in the Nirnaeth and that he held the Gap, which was a very vulnerable position), while others have difficulty viewing him like this. 

I don't know if I'm being of any help, but you might find Dawn Felagund's character biography of Maglor quite interesting. :) 

Maglor seems to have done quite a lot of riding at one point--or maybe it's just his people at Maglor's Gap who did it rather than himself. Also, he does seem to go hunting along with his brothers and cousins at least occasionally. But he could still be more sedentary and chubby compared to other elves--after all, this is Elrond thinking about him, not a hobbit like Bilbo.

I like what you did with the bracelet!