So I really do not want to incur any legal trouble because of my own negligence.

However, due to their negligence and language barrier, the land has been vacant for years and they ended up getting thousands of dollars of fine and bunch of violations because the homeless literally built a house on the land.

You can always pay off a 30-year like a 15-year and the difference in rates is negligible.

Of course I don’t want to spend too much here but I also want to make sure I cover major issues, create a checklist of what’s done and avoid any liabilities for negligence.

@Phillip Rosin I would replace the water heater due to its age but I would not move it unless the cost is negligible.

I know that the landlord can be considered liable for falls/ slips if/when it was deemed they were negligent in addressing an issue that caused the fall/ trip (ex. knowing of a leaking pipe which caused floor to be wet) However, in this instance where it was due to actions of the tenant, would you initiate interventions to reduce the risk of future falls? 

As a general rule, if you do work to improve the building it increases the assessed value.But the amount could be negligible in the end and there could be a delay of a year or more until it affects the assessment/taxes.For example, if the assessed value increased by $10,000, taking into account the 40% discount on assessed value for owner occupants and applying the tax rate of 24.56, would only result in $147 more tax per year.

Also does the motivated sellers very own negligence of terms & agreement means I keep the earnest money of the cash buyer or not ?

It is the rental income that reflects the value of the investment @Rob Bardwaj Comparing the condo fee is negligible.

Obviously pricing structures are a bit different but if one is much better than the others then pricing difference should be negligible