what matters for a learner? bigger or more volume?

hello! im dave is this is my first post. im super stoked to start learning to surf, and im just sort of gathering all the information i can so i can avoid making a bad purchase, mistakes, etc.
pretty much everyone ive spoken to has told me that i need to either go big for a first board, or find a funboard. im about 145lbs, and 5'9". yesterday i strolled into ZJ boarding house in santa monica just to look. got into a conversation with a salesman, who pretty much reiterated what i should be getting. but then, he told me that although a bit pricey, that the best option would be this 6'6" firewire addvance board, and that he has taught people on that exact board. its obviously much shorter than anything ive been recommended before, but i guess has the right amount of float for someone my size. i just thought id ask what some of you guys think. id like to get on a shortboard one of these days, but im willing to do it right and go through the whole process of learning to surf the right way. if i can really start on something shorter, that would be cool. what say you?
pretty much everyone ive spoken to has told me that i need to either go big for a first board, or find a funboard. im about 145lbs, and 5'9". yesterday i strolled into ZJ boarding house in santa monica just to look. got into a conversation with a salesman, who pretty much reiterated what i should be getting. but then, he told me that although a bit pricey, that the best option would be this 6'6" firewire addvance board, and that he has taught people on that exact board. its obviously much shorter than anything ive been recommended before, but i guess has the right amount of float for someone my size. i just thought id ask what some of you guys think. id like to get on a shortboard one of these days, but im willing to do it right and go through the whole process of learning to surf the right way. if i can really start on something shorter, that would be cool. what say you?