I would say... 今日という日はなんて美しいんだろう。　そしてあなたも、なんて美しいんだろう。 or simply 今日は美しい日だ。そしてあなたも美しい。 Because I prefer the word beautiful here to be translated into the same word, instead of two different words. And the word kirei can't be used for a day. Subarashii would also work instead of Utsukushii.

つばらしい is like saying wonderful. I think it would be more appropriate to say '今日はきれいです'. But be considerate that 'you are' could be inferred. For the latter sentence, is this for a guy? Otherwise, try using '美しい'，'かわいい', etc. to be more expressive. Kirei also means 'clean' so... maybe not here?