In terms of determining fair market value, it’s not at simple as dividing NOI by a cap rate.

Can someone help me with understanding how mobile home parks compare to single family homes in terms of return on investment?

Not too bad of a renovation, in terms of cost to repair. 

What I can tell you is there are many different areas to both cities and you can find whatever you are looking in terms of living situation.

I'd also be careful assuming the market is going to cool down - depends on who wins the elections AND what the government will do in terms of pumping money into the economy (if that's the case, we could see inflation and that will not bring the prices down... 

In terms of other areas you can consider, I think Revere by the T is an attractive option, you can look at Medford (both wellington side and West side depending on your budget), Everett (West Everett is right by Wellington), and Watertown.

Have you found one site better than the other in terms of the quality of leads?

Confirm that the provider has experience with the particular investments in which you intend to invest your retirement funds as you very likely will have questions in terms of the mechanics (e.g. how do you invest in real estate, etc.).4.

But this is commercial and we are still new so I am not sure if the same rules apply in term of accepting rent in advance? 

The first thing is to set expectations with your investors in terms of the returns - while these properties are good in terms of overall returns, it takes time and effort to bring it to a stable state.