Square foot pricing has absolutely no place in electrical bidding. If you think about it, square foot pricing might be related to a field such as concrete slabs, carpet, tile or other fields involved directly with areas.
If you must, you could do your take-off of material, labor, sub-contracts [rental fees, permits,, etc.] and overhead. Add your profit. Then divide by the square footage and get the stupid, real estate slime number and use that.
But going backwards and multiplying the square feet by some mythical number isn't gonna have any relation to reality. How much does a Fiat cost per pound?

As for the phone. HVAC, etc., you wil have to look at the plans, specs and contract. What is included?
~Peter