Looking forward to reviewing these options.Here's the PA law: https://clsphila.org/housing/security-deposits-in-pa/Any bank account will work.

I know that the general guidance is that emergency funds aren't to be invested, but given our financial security and the fact that we already have a personal e-fund in a safe, non-volatile location, would it still be crazy/unwise to invest this 15k in an S&P500 index fund in a brokerage? 

There are many good locations - I'd suggest that you play around with the "Market Finder" tool at the top of the screen here, included with your pro membership. 

Traditional bank loans can be slow and have strict requirements, while hard money and private lending seem to offer more flexibility.For those who’ve secured funding before, what’s been your experience?

Here's the deal: You don't need to withdraw and return the current security deposit just to collect the additional $100.

It's mostly Class A properties, a few Class B.You may find the below copy & paste info useful in addressing your question:----------------------------------------------------------------------------------Recommend you first figure out the property Class you want to invest in, THEN figure out the corresponding location to invest in.Property Class will typically dictate the Class of tenant you get, which greatly IMPACTS rental income stability and property maintenance/damage by tenants.If you apply Class A assumptions to a Class B or C purchase, your expectations won’t be met and it may be a financial disaster.If you buy/renovate a property in Class D area to Class A standards, what quality of tenant will you get?

@Brady Bitter First what are you calling "securities"? 

There is a ring camera system that has a job site security package as well some of my investors use for their projects do not have internet it works off cellular connection. 

Local investors can now get additional discounts by moving up the food chain and buying as notes and, on mortgages secured by vacant properties, utilizing the preREO strategy to generate revenue during foreclosure process.

Maybe if you had a good, secure location to store things you could pre-order stuff you think you might need for your next project(s) and stockpile it.