Rolling shutter business

hi
sir we are into rolling shutter business, we manufacture rolling shutter door and sell PAN India. i have the following query:
1. GST rate applicable for our finished goods is 18%. we add installation charges and freight charge separately, will it be taxable? if yes, what will be the tax rate?
do i have to raise a separate service invoice or can i add it in the same invoice alongwith the finished good.