Maining multiple characters in fighting games, is it practical?

Well recently me and my brother were at it again, this time about the concept of using multiple characters in fighting games, we mainly play Blazblue or MVC3 and he likes to use multiple characters all the time, not really a problem, except he kinda gets mad when he loses, my view is that it is good to USE all the characters at least once to get a better feel for them and the game, but you should not try to main more than 3 depending on the game. My brother's view is that it is disrespectful to the company and a waste of money to buy a fighting game to only play as 1 or 2 characters competitively. He also says it gives him a better strategy when fighting against the character. I keep on telling him how rediculous it would be to be able to use every character just as well as your main but he believes it is practical. My main question is in your opinions how many characters should one try to use on a competitive level? And how many is too much, or is it common for people to main more than 2 or 3 characters at a time? What are your views on the subject?

Can someone please explain the difference between Ryu and Ken?

For a long time now me and my brother have argued about Street fighter being diverse or not, I think it is but he thinks half the characters play the same, the main argument is ry and Ken "Ken is just ryu but with fire" or something like that. I believe that street fighter characters are unique yes moves are similar, but they play different. I was hoping someone can give me a good explaination on how Street fighter characters don't all play the exact same just because a lot of them have uppercuts and hadokens of some kind. I didn't feel this needed to be a thread so I made it a blog.