The word 'Welcome' is pretty useful. I advise you to use it in expressions like 'You're very welcome in my country'. You could also say you hope they enjoy their stay, and that you look forward to working with them.
By the way, it's 'new arrival' or 'newly-arrived person'. An 'arrival' is nearly always a person, though when you say 'the arrival of...' what arrives doesn't have to be a person.
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