My Job (First Exercise)

I have been working for a toy's shop for four years. Seven poeple work for me; actually I'm an assistant director, and that's it's really interesting. I must lead and motivate the employees. I'm very keen on doing this, but the most difficult thing is to make the difference distinction between colleague and friend because during this these four years, my colleagues became to my friends !
I like working for this society {"organization" might be better here}, but I want to become a director for a the biggest* store name.

*Since you're working with comparatives, there's only one that's the biggest, i.e.:

"I want to become a director for a bigger store name" (there are several stores that are "bigger").

But it's: "I want to become a director for the biggest store name." (there's only one #1 store)