Прежде всего я хотел бы поблагодарить тебя за ....

Sounds nice!

Alex I don't feel confortable about the: "no difference".

For example a client asks me. How I could improve the serives of my company.
And I answer: At the beginning you should improve your marketing.
I think in this case сначала sound as: "from the beginning" and not "at the beginning".
I am wrong?