My suggestion was going to be to prorate the monthly rent for sake of starting the relationship on the right foot. 

Your first few deals not only get your bank roll going but they also set you off on the right foot if you have success.

How much is a reasonable price per square foot for new build?

I know there are risks: breaking my window, breaking a tenant's car window, tripping over a cypress knee and cutting off their own foot, etc. 

Her 1600 sq. foot, spec house, without a garage, sold in one week for $383,000.

Well he did and I can tell you getting a referral and being able to Mention Mike as a Colleague got my foot in the door with a much bigger bank.

I am wanting to start out on the right foot.

Hopefully you did not pay too much for the dirt. 1 acre is optimal these days because of desired double to triple drive thru for QSR.It can become a problem because if they make the building smaller you get less rent but they do more sales.Example a QSR used to be 3,000 to 4,000 sq ft but now instead wants double drive thru's as not many go inside for fast food like pre-covid.If you get 1,000 a foot less at 30 a foot you just lost 30k NOI and now at 5 cap example paying all cash NNN once developed you have lost 600k value.It can fine as long as you do not overpay for the land.

But you're on pretty good footing.

Everything he did would be his foot in the door, but nothing ever panned out.Wholesaling rarely pays off, and it is even more rare to make a living at it.