Thank you, that’s really helpful. Is there anyway I can protect myself from the tenants claiming the amount of security deposit given? Can I request something from the seller that will be legally binding what security deposit (if any) has been received etc?
The estoppel is a means of confirming the terms between Seller and Tenant. If you can't confirm them, then you'll have to accept the risk that something was innaccurate or hidden. I don't think there's much risk. The Landlord may claim the Tenant paid $1,000 for a deposit and the Tenant may claim it was $2,000. You'll have to deal with those issues when they occur.
If the numbers are good, the numbers are good and you should move forward with the purchase.
Here's a NJ guide to removing Tenants: https://www.nj.gov/dca/divisions/codes/publications/pdf_lti/...
The day you close on the purchase, deliver a written introduction letter to each tenant with instructions for paying rent, reporting maintenance, etc.
At the same time, notify them of the pending changes. Tenants that are 50% below market were probably never screened, likely to be problematic, and unable to afford the increase. I would give them notice to vacate within 60 days. Offer incentives if they leave early (e.g. give them 60 days to move out but offer $200 bonus if out two weeks early, $400 if out a month early).
If they fail to move out, have a good eviction attorney lined up to start the eviction on the very first day legally possibly. Be kind, but be professional. Tenants typically don't screw around when they see you mean business.