With only 5% appreciation factored in (to be conservative), my ROI on my 20% down payments is around 80% on all my properties.

Maybe if you're lucky you were able to negotiate with the other tenants to get those units up to market rent as well, further pushing the value upwards (of which there are a few tricks, although the deal would need to make sense without this factor as it is not guaranteed.

In regards to tenants already being in place within a unit - my encouragement is to not worry too much about this being a LARGE positive factor.

This is usually the determining factor when calculating deals and knowing if it’s worth it, but I don’t even know where to start.

If it’s a ten cap after all cost factored in and 4% interest rate your return for 25% down with 0% appreciation is 28%.

@Matthew PurvisWhether you owe Uncle Sam for taxes depends on a number of factors.

This will depend on a lot of factors like how many units there are, if it is owner occupied, etc. 

Since you weren't the owner and never foreclosed how you factor into this, where is the original owner is this, etc.

The other factor here will be your income - it'd need to be looked at.

What key factors do you look for when renting to tenants?