with respect Falcis :
but if you have to look for help / advice, then maybe the job is beyond you .......

get an experienced IT consultant in to advise / design
pick their brains
get involved
learn everything you can, as an opportunity to oversee an install of a complete new network doesn't happen everyday.........

it's a business I assume ?
so do not take on what you do not comprehend.
as if it did go **** up, so would your career