My initial approach was to stay leveraged around 60-70% during the "growth" phase of my portfolio, basically until I reach my unit goal and de-leverage after that.

If you get to the budget phase it’s more than just the building.  

Can my offer have contingency for phase 1 passing in addition to rezoning approval?

There are some things like section 179 depreciation that may also benefit you (which is phasing out, we're at 60% for 2024). 

I am a new investor that is in the learning and planning phase.

It's a great skillset to develop, but is ultimately just another day job.I think one of the best places to start when you are in this learning phase is to get around other investors that are actually doing it.

Most each real estate syndications (group investments) go through a progression of stages.All should have a clear beginning, middle, and end.Here are the 4 phases for a typical syndication deal:Phase 1 - AcquirePhase 2 - Add ValuePhase 3 - HoldPhase 4 - Sell 💰The sale is arguably one of the most important phases!

I would be in charge of running the project, construction, all costs, I would float the project.Once the first unit is completed we would put financing on it and the proceeds would then fund subsequent phases, enabling us to progress through the project over a multi-year timeline, likely spanning 3-5 years.Estimated my construction cost would be 350,000 per building (pure cost no profits).

People go through life phases. 

Even if something is discovered in the inspection phase etc, there still is an obligation to purchase.