Seeing as we're using rough guesses to calculate the new Yam Stand's capacity, here's my uneducated calculations
The new Yam Stand has 37 rows and, if your figures are correct, there are 208 seats in each row.
Hibs Main Stand has 34 rows (16 upper, 18 lower) and a capacity of 6,100
So, that's 3 rows more, three times 208, so 624 seats.
Add the 624 seats to the capacity of Hibs Main stand and you get 6,724
Add that figure to the capacities of their other stands and it makes their stadium capacity roughly 19,300
A very rough estimate but there you go.