The rule of thumb is purely intended to be a (very) basic first step to make the real analysis actually doable from a time perspective.  

If a development is purely for senior citizens, then it can discriminate based on familial status.  

Is this just purely a case of semantics? 

However, from purely a gut feeling, I agree with @Martin Z. that I'd rather split the inheritance of 4 properties into 2 for you and 2 for your sister. 

Title insurance is purely for issues that are not apparent today, and may surface in the future.

I think it depends on the type of housing- pure student housing or housing that could also be market rate?  

We are older and my husband has an excellent W2 job, so we do not need it as income, it is purely a long term investment.

Aside from those, you have "pure" college towns like State College.

Just the pure economics of starting/developing a MHP is not beneficial for most people as your hold period will have to be several years without any return...so unless this is okay with you and your okay with developing the land, bringing in roads, water/sewer, electric, cable/internet, developing the pads, and bringing in the homes, your going to be in the whole at least 20k-50k(includes home price) per pad before you even get this up and running to full or close to full occupancy.   

Is this arrangement purely tagging onto Tom's reputation?