When a tenant breaks the lease early the landlord is required to try and rerent the property to mitigate the balance owed by the tenant.

This is essentially a higher risk tenant (at least potentially) so you should charge more upfront to mitigate that risk.  

One of which resulted in the discovery of a backpack meth lab which required mitigation in the end for us.  

That being said I would not buy this property unless you know something mitigating factor that we do not know about...

Make sure you are comfortable and have a solid plan (and multiple exit strategies) in place to manage and mitigate those risks and the IRR you get adequately compensates you for taking on those risks, your time, and your money that you will be putting into the deal, given your other options.

Its all about cash flow, mitigating risks for all parties, and showing you know what your doing and are ready to take on the challenge.

From my perspective the 4 Residential units would anchor the property and mitigate the risk of having the one commercial unit.  

So the risk of finding a suitable replacement is mitigated.2.

Is there anything else I should look out for to mitigate my risk?

You might not ever find the "perfect" deal, but keep looking for the one where you can mitigate the down side.