Thanks for your time?

Hello,

While finishing a formal letter, what should I write that will mean "thank you for spending your time reading it", is it okay if I say "thank you for your time" only? Can I then end it like "sincerely"?

And another thing is to start the letter, if I don't know the name of the person I will say "to whom it may concern", I know this. But, if I do know the person's name (and this person is a professor), what should I say? Mrs/Mr kind of things?

I am very bad at these kind of stuff in letter writing.

I hope I am posting to the right place.

Thank in advance for your help.