Assuming the land cost was affordable and clear, what major financial challenges can come into the picture upon the decision to develop a small complex and is there a "play" these days for developing smaller complexes (30-40 units)?

Depending on if you itemize your taxes or not and if you can afford to be cashflow negative you may want to try for a shorter loan. 

As for affordable -- possibly tax foreclosures? 

My mil is in a tricky situation with downsizing and being able to afford a small home in an area close to family.

I am in a similar boat where I can afford to be flexible and creative with my house hacking strategy.

As far as what I can afford I'm curious about you opinions on this as well, I currently make around 130k, and within a few months I'll be closer to 160k. 

The ones that are somewhat affordable need a ton of work or are in areas where you really wouldn't want to live.

Most of them had moved to lower priced Cities because they just couldn't afford to live in NYC anymore.I also had another friend that bought for cash flow out of State.

He basically said if someone was able to build an HOA management platform that was both user-friendly and affordable, there would be a real market there.Having deep knowledge of relational databases, java rest APIs, user-friendly UIs and just building/deploying web applications in general, plus having built these types of systems many times before professionally -- albeit in different sectors/industries -- I’m seriously considering a side project to build some type of HOA SAAS (software-as-a-service) product that will hopefully make people’s life’s easier without costing them a fortune.My question is, before I invest time and energy in this, is there actually a market there?

Lots of NYC investors look downstate because the homes are much more affordable than NYC.