Depends on your assets, lifestyle, resources, desires.  

“Without a sense of urgency, desire loses its value.”

Seek out regions with robust population growth, a variety of sectors, and job growth.Make contact with nearby property managers, real estate brokers, and other investors in the desired region.

You want a desirable location plus with minimal sloping/grading issues and minimal trees.

You had one desired outcome that was outside of the parameters of what we were able to make a reality.

one option would be using it to BRRRR enough properties to generate the desired amount of monthly profit in the end. as far as cash vs down payment, if you want to build more wealth over time, i would definitely use debt so that you can buy 'more' ($) real estate. leaving it in index funds isn't a BAD idea, but if you have the resources (time/knowledge) to invest in RE & do it wisely, you will likely come out so much farther ahead. another question here is, how much monthly income are you looking for this nest egg to generate in retirement?

Growing Demand for Affordable Housing: The ongoing shortage of affordable housing options drives demand for mobile home parks, particularly in desirable locations.

I could definitely buy a multifamily by myself but it would be in a less desirable area that we might not feel as comfortable living. 

Buy a neutralizer, spread it around heavy, poly film it, come back in 24 hours, ozonate if there is still smell (likely for a couple days or more depending on smell and ozone capacity of machine), then you’re probably sanding and throwing down whatever stain /polyurethane you desire.

Less desirable neighborhood but in-filling quickly.