Yes, this can be a huge time saver especially if your jurisdiction considers this an "addition" instead of a "new construction" which generally makes it easier and faster to get a permit.

I would try to get an optional 15 day extension with additional EMD, if possible. 

These are professionals with additional training and a stricter code of ethics.

I’m just getting things started and want to get into ‘buy and hold’ properties to bring in some additional cash flow.My wife and I have a decent amount of funds set aside, but I was wondering if it makes sense to open a HELOC on our primary residence and utilize some of those funds as well for a down payment.

You can list your unit on there, as well as do background and credit checks and collect rent.In addition to asking a local realtor for the rental rates, you can look at the rents of similar properties in the area, which you can find on places like Zillow and Apartments.com

Additionally I invest purely for cashflow.

What is relatively new is the “mortgage stress test” where banks shall add an additional 2% on the top of the landing rate to make sure people can truly afford it.

In addition to what's been said above, the invoice should clearly state the address where the work was done and your company's name.

We were at a loss for how to get cash to purchase additional property, and are considering taking out a mortgage on the duplex.

Plus don’t forget closing costs on each not to mention most properties need at least a little work and additional cap ex to turn into performing assets.