You could hire a project manager  and source your own subs  . 

They know how to get deals, renovate, push equity, screen tenants and manage.

But if you took a HELOC, which tends to have relatively high interest rates, your blended rate (the average of what you're paying on your mortgage plus the rate on the HELOC) would likely be in the same range as today's mortgage rate.You'd also only be renting out one unit, but by selling it might allow you to get more than one additional unit and still grow your portfolio. 

I don't have any experience in construction, property management or managing a project like this.

Currently, I manage three villas for rent.

My husband and I are interested in starting a real estate portfolio, but figuring out what's the best niche in this area.

I work with these types of assets and Partner With @Alice Horn of Villa Key management.

A strong managment agreement between tenants..   

Do you recommend or work with any property managers in Waco? 

If you can figure out how to get a quality asset and manage the risk you can do great.