In french we don't use "my friend" as English speaker do. It's a third person use , e.g : when you talk about someone (who is your friend), Not a second person use (e.g: when you say directly to someone he is your friend). Except if you are really really close with someone and in a very emotional conversation, you'll never casually label him "a friend" to his face. It is seen as false, or hypocritical, or mocking. But most people know only non-native speaker will use "my friend" this way, so it's kind of charming.

BUT..

There is sort of a slang word (not a pejorative one) we use that exactly has the meaning of "my friend " in English. It's "pote" (or "poteau"). So your sentence should be "Merci beaucoup mon pote, c'est fantastique d'être ici".. It's a popular level of language. You wont sound harsh, or insulting but it's not appropriate in a formal conversation. I guess it would translate to "my bud" (or "my buddy").

Always pleasant to see English speaker going the extra mile to learn that convoluted, complex language full of exception, and stupid rules.