As my own employer....I can set up a $2 to $1 matching contribution to my 401K.... so I could put in the max $18K and my LLC would contribute another $36K. 

Yes there is partial exclusion available but you need to meet either employment, health, or unforeseen circumstances.

Here's the huge benefit to passive income from rentals- It's not subject to self employment tax like your flip income is. 

Definitely include property management fee (Around 10% for that size) in your operating expenses.

A large percentage of buildings that are not residential have flat roofs, especially when they get past a certain size it just gets impossible to have sloped roofs.

You are currently only making $416/month on the duplex so that should be taken into consideration on what size of loan you take out.If you take out a loan would the money be better spent on the addition, or would it be better spent on another property?

I can send you a Rec based on the size property

This is the message from Wells Fargo:"Purchase contract shows that buyer Nina Ibrahimbegovic (non-borrowing spouse) is the buyer’s agent and is employed by the listing agent company Charles Rutenberg Realty.

VCU and USC are similar size universities, so student rentals are a greater percentage of the market in Columbia vs Richmond.

I can do this work cheap because of my employer, and access to equipment.