.- Im thinking of not charging security deposit because of all the strict MA laws and just using the last months rent as a sort of security deposit, thoughts?

As a professional property manager, we do move-in and move-out inspections and if those photos do not match, the tenant is responsible.

All in order to match the savings from the first lien HELOC strategy.  

When you renew, you can add a pet deposit with the new lease. 

. - Collect rent every way possible including letting tenants deposit cash into a bank account.

You can target a specific tenant segment by matching the segment’s housing requirements.Each tenant segment has specific housing requirements and is unlikely to rent properties that don't meet all these requirements.

In our24 years of experience, managing almost 100 S8 leases currently, the average S8 tenant has a FICO under 580, numerous collections from utility & cell phone companies, doesn't want to pay a security deposit, much less an application fee and claims they don't know how to fill out their S8 paperwork despite being in the program for several years - hint: they want YOU to do it for them.Most, not all, are eligible for government assistance due to a funeral-march of bad choices.REALITY: you are trust trading one set of problems for another.You can succeed with S8, but you need to understand the challenges and plan accordingly.

The company doesn't really have a "credit score" or "eviction history" so I'm thinking about asking for 1.5x or 2x monthly rent as a deposit (we normally do 1x month rent) just like I would for a tenant without established credit history.Thanks!

I have no responsibilities - other than reading regular reports and (hopefully) depositing checks. 

An estoppel is just a verification of rent and security deposits.