Translation:Merhaba, hoş geldin!
From what I've read in the other threads, merhaba is more formal than selam.
hoş geldin: to one person only, and it is informal
hoş geldiniz : to several people or to one person but in a formal way
It is supposed to be selam hos geldin since rica ederim is like saying you are welcome after a person said thank you but here you are welcoming