It’s correct and formal but if you say it out fully the way you wrote it, it’s too formal for many situations and would sound odd and unnatural. In English speaking we often use other ways to express sincerity and formality than grammar. For example I wanted to thank you for the report, I really appreciate your help. Or I’d like to thank you for the report. Using the contraction makes that closer to your second option.

Yes, the first sentence it is both polite and correct. In fact, it's more formal than just saying "thank you".

Both of these are correct 😁