They were a law firm who hunts class action suits to go against companies. 

What would be the best course of action to sue them for non-payment? 

After a grace period of 1.5 days give another notice and mention legal action or law enforcement5.

What should be my course of action- I really don’t see the tenant appreciating what has been done and would rather break the lease. 

That property is now a reliable source of rental income and a constant reminder that success starts with taking action, learning on the fly, and embracing challenges head-on.

Now this is with an uncontested legal action..

I consulted with a real estate lawyer a few times this year who said it's very hard to sue for negligence and they advised against taking legal action, especially since the property manager at least followed through on the eviction and repairs.I've now asked the property management company to apply a $4k credit for all the challenges I've had working with them.

I never make a loan, no matter the equity position, that the past actions of the borrowers lead me to wonder if they will be likely to pay me back. 

Taking these two pieces of info will tell you how long you will take to get an offer, so if you go past that you should lower the price, and then the other action item would be to starting off lower than all the other properties if the condition is better than your condition.

Non stop action taking and never giving up plus always making sure we give our absolute best to clients and always reply never making anyone wait and go to a competitor :)  I have Ads, I have a lot of social media posts and updates on all social media platforms daily.