Use the HELOC funds for another investment strategy such as funding fix and flip projects.

Are you planning to take on another project like that soon?

I golf, play a lot of softball, run most days, walk my dogs, do some real estate projects.... stuff like that. 

Feel free to DM/call me so i can help you with your first F&F project.

I would like to be prepared for a larger multifamily project. 

Example: invest in syndications / short-term rentals / oil & gas wells / solar projects / conservation easements, and so on, due to the tax losses they generate.

A picture is worth a 1000 words and a project we helped someone on in the UP was able to gain support and approval by getting renderings done showing what the finished project would look like.

If your "estimate" works for you and your "high estimate" is still workable for you, then you can feel confident that if you use good project management practices that you can manage the project to somewhere between those 2 numbers at worst.

And if they are a hobbyist/part-time builder, then they should engage the proper professionals, i.e. a title officer, civil engineer, architect, contractor et al to assist in reviewing the project's feasibility.

Look for areas with solid rental demand, typically in Blue Collar America, where BTR projects are particularly appealing.