You are just learning and might as well not add the stress of high interest mortgage on top of it.I also agree with @Jonathan Greene that I would go for something with potentially less upside but an easier renovation. 

I was considering on waiving all late fees and reducing my rents across the board by 20%.

For those with experience, what is your big picture approach / policy / advice for how we should handle our tenants and these requests for reduced or no rent as they come in? 

As a proactive measure we reduced their rent by 50% for the month of April and will look at May in a few weeks.

You can follow the law and post notice, but I think it's waste of time and just puts more stress on tenants.

It isn't the same because there are different problems this time, that may or may not affect RE, if we don't go into a prolonged recession we are likely to maintain the status quo, if we do the likely culprits to affect RE are oversupply due to people forced to sell because of job loss and a reduced buyer pool also due to job loss.

As I tried to stress, I am very naive on opportunity funds.  

You can put more than 20% down to make it cash flow, but that reduces other numbers like your cash on cash return.

Step 1 see if the seller is willing to reduce the price.Step 2 challenge the appraisal.

I believe the virtual tours are here to stay and will probably reduce the number of questions future tenants will have.