"Headcount" is not incorrect you could replace "number of employees" with this word if you like. Personally, I don't like the word headcount: this word is sometimes used for counting cattle or sheep, or pigs on a farm. As you use "professionals in the first sentence (a word that gives value to individuals), using headcounts seems to me to slightly devalue the people working in the company: just numbers rather than individuals. As I said, it's not wrong, I just don't like it in this context...

The Ukrainian office of the company employs up to 80 professionals, with the total number of employees worldwide being about 400.

Headcount is fine. No sure about 'up to'. That suggests the number varies but is never more than 80. Maybe 'around' or 'approximately' would be better. Or simply say 80 professionals, no one is going to count exactly!

Hi Sasha! Yes, headcount works here. You could also say the 'staff body'. Also, you could use or 'staff, including supporting' staff. You could also use the word, 'team', instead of staff, i.e. The company's worldwide team consists of... Or The company's worldwide staff body consists of Hope this helps! Let me know if you need any more help 😀 Miss Maria