Life is about trade-offs, so figure out which ones fit you.

Any specialized trades/subs will be under the umbrella of your selected GC. 

I ended up selling the larger buildings and traded them for 1-4 unit Class A properties in better locations.

Try explaining that to the IRS.Schwab will not open a trading account for your IRA-owned LLC, nor will most of the mainstream brokerages.  

A heloc add another trade line to your credit and can cause issues with fico scores dropping or DTI going up causing issues with credit limits or other risk based issues.Regarding the $4K in closing costs that is pretty much the standard for a loan amount of $100 to $150K.

I'm not in an area where lots of 70k sq ft industrial properties trade hands all that often, but there's lots of smaller industrial properties.

If you trade into a more valuable property, as you did here, the increase in value is added to your old basis.  

All the trade websites say that in the end they're only a tiny percentage more expensive than regular concrete block because the labor costs go way down.    

It's also quite a bit more complicated than "this qualifies for 5 year and this doesn't qualify" since there isn't really a "list of every possible asset and it's depreciation life" most assets that qualify for 5 year fall under asset class 57.0 assets used in distributive trades and services.

This is sufficient size to have reliable trades-folks do good work at reasonable costs.