The plan was to knock it down and construct a new building, one fitting for the style and architecture of the neighborhood. 

Unless you are VERY confident the house used as collateral will retain its value, I would stay away from a HELOC at this time. 140k could be gathered through a syndication style agreement with any investors getting somewhere around 8% as a preferred rate.

After managing these types of garden style apt. properties for years, I always wanted to get on to the ownership side.

That said, you can do and FHA203K or a Fannie Mae Home Style Renovation loan or any number of owner occupied type renovation loans offered by various lenders.

Purchase price: $140,000 Cash invested: $450,000 Started with a raw piece of land Built a town home style duplexRefinanced out the money to build another What made you interested in investing in this type of deal?

The furniture and decor took me 2 months to style it a certain way.

These style deals were impossible 6 months ago but we're seeing them more now.Last- if your goal is specifically to generate the highest level of cashflow possible you'll have to look at more esoteric management options (rent by room, STR, Travel Nurses) or in markets with more favorable rent:price ratios. 

The kitchen cabinets were all wood but an old style so we flipped the doors around and painted the cabinets to give them a modern look.

It was a learning experience and planning every detail and researching what type of styles sell quickly in that area.

Or more likely (an assumption based on location and typical age of the home style you describe) it was built before codes were a consideration but was still legally constructed as it is currently used.