[Mika]

Minna is spelt with two n's, because it's written like this: みんな。

If you would like to say "very" you can use Totemo if you like. Totemo samui desu. If you ever need to negate and use "Very", Amari works well. "Amari atsukunai desu." would mean "It's not very hot." for example. Chotto means a little. "Chotto samui desu." is "It's a little cold."

What about you is easiest as "Anata mo?" Which means "You as well?" And can be used for any question like that. ;3

And since you're using polite form and not casual form, it's more natural to say "Minna-san" in this context. To keep all the grammar matching.