Some may require a waiting period of one to two years before leasing is permitted, while others may prohibit rentals entirely as outlined in their bylaws.Always know the property’s potential for annual rental income and ensure the numbers work.

I assumed you'd use HELOC for down payment + another loan for the rest. that is 100% financed. 

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?

Just remember anyone who has acted as your employee, attorney, accountant, investment banker or broker, or real estate agent or broker within the 2-year period ending on the date of the transfer of the first of the relinquished properties is considered your agent and is disqualified from being your QI.So definitely ask them for recommendations but they cannot act as your QI on the exchange. 

Most of the time but not all of the time, I visit the property during the due diligence period.

While there is no statutory holding period to qualify, it is important that you be able to demonstrate that your intent was to hold. 

The only issue I've had is a small period where the laundry pods would always be empty at turnover. 

In exchange, I have first rights to sell the property through a power of attorney. once it sold, the seller get his agreed price, and I get the rest.

The crypto can be considered as EMD or down payment, the rest of the transaction will happen just as if you were running a traditional transaction.If a seller is completely against the idea of receiving crypto, you can always use a service like Bitpay to convert the cryptocurrency to cash.Last but not least, I always ask clients... why sell your crypto asset when you use it to secure a loan?

The timing of people most apt to say "F-it, I'm done with this stuff, I'm gonna take the $ and run" is in that 90 day period.