Or how to put the unpaid rent on their credit score

When it comes to these types of auctions by the sheriff, is there a waiting period that must be observed before rehabbing/renting the building post winning the bid?

Closing costs + rent ready costs + lease out costs - those you need to be compensated for and new investors are always surprised that they can add up to 5 or 10 or 15K.  

To eventually also cash flowing as rents increase. 

There was quite a bit of unused land and the zoning gave me some flexibility if I wanted to expand various aspects of the property.Also the self storage units were all below market rent and the seller was willing to finance at a decent rate with a 5 year balloon.

Two other key aspects that worry me about Japan are (1) generally depreciating values of real estate and (2) generally decreasing rents. 

When rent is too low it speeds up the leasing.   

Time overcomes low cash flow to some degree... rents go up while your mortgage stays the same and your tenant pays down your mortgage.  

I don't see an exact location in the OP, but if this is even remotely considered rural, you are adding another LTV reduction. 

How many bedrooms does it have and what do you think it'll rent for?