Hello tuscanlover! I'm new to the forum but I'd be happy to answer you
You are indeed very lucky as the Vasari Corridor will be open just until the 10th of June included (excluding the 2nd of June as it's a festivity), so right in time for your visit!!
There will be guided visits, but unfortunately only in the Italian language; and in particular 6 visits a week will take place: 2 on Wednesday and 2 on Friday at 2 pm and at 4.30 pm; and 2 other tours on Thursday at 9 am and at 11.30 am.
I suggest you reserve your visit quickly as the number of visitors is very limited, you should call Firenze Musei at +0039 055294883.
I hope you'll be lucky in finding a spot for your visit!