Under contract for a 20 unit

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Ok so somehow I miraculously got a 20 unit under contract.  I already have a small commercial residential I bought two years ago and I’m trying to make sure my DD period I get everything covered.  I have an inspector I’ve used before.  Is there anything extra I should be looking for besides the standard water, electric, roof, parking lot, and structural?
It is in septic and well.  Should I get those both inspected?  If so what type of company does well inspections?  Just trying to make sure I don’t miss something that causes a 100,000 capex expense that could of been caught beforehand.  

Also as a side note, what’s everyone’s biggest deal they took down by themselves?   Am I trying to eat the whole elephant.