Now multiply the number if piers by $250. 29x250 = $7,250.Now add $200 for permit & $400 for Engineer's letter (yes, both of these are required by the City). 200+400 = $600Total foundation price = $7,850.

However, Using the gross monthly net per property, with a multiplier of 1.8 and then multiplying by 12,  I can’t fathom this $675,000 number.  

When he entered the gross monthly income to the rental property gross monthly income, he multiplied the $725 by 4 which showed grossly month income of $2,900.

It wasn't meant as literal 20 doors exactly, but more an expression of wanting to multiply what I started with.But I get where you're coming from in that last paragraph.

The amount of work and stress will multiply so I would just be cautious about that

You can use monthly periods and the resulting IRR equation will deliver a monthly IRR which you can simply multiply by 12 to find the annual IRR.  

For MTR - look up the same property for LTR rates and  multiply it by 30%.

So you'd be multiplying $20, 000 by 20% to get $4,000.

The managing member needs to be able to understand the depreciation + rental income for the year and multiply by the partner percentage of profit/loss. 

When you enter the address of a property, the site estimates the rent by multiplying the average area $/SF by the subject property's square footage.