Just wondering if owning 10 properties with 5% equity in all of them is a dangerous thing or if that sort of portfolio structure is fine as long as the investor has sufficient cash reserves?

I recommend a Post Compliance Lead Determination (PCAD) every 5 years or so.Here's the law (emphasis added by me):460.100: Duty of Owner(s) of Residential Premises (B) Whenever any residential premises containing dangerous levels of lead in paint, plaster or other accessible structural material undergoes a change of ownership and as a result a child younger than six years old will become or will continue to be a resident therein, the new owner shall have 90 days after becoming the owner to obtain a Letter of Full Compliance or a Letter of Interim Control, except that if a child younger than six years old who is lead poisoned resides therein, the owner shall not be eligible for interim control, unless the Director grants a waiver pursuant to 105 CMR 460.100(A)(3).

If you delead, and maintain the standard, you will be in the clear.Here's the law (emphasis added by me):460.100: Duty of Owner(s) of Residential Premises (B) Whenever any residential premises containing dangerous levels of lead in paint, plaster or other accessible structural material undergoes a change of ownership and as a result a child younger than six years old will become or will continue to be a resident therein, the new owner shall have 90 days after becoming the owner to obtain a Letter of Full Compliance or a Letter of Interim Control, except that if a child younger than six years old who is lead poisoned resides therein, the owner shall not be eligible for interim control, unless the Director grants a waiver pursuant to 105 CMR 460.100(A)(3).

Still, no lender can use the borrower's current status as a reason to deny a short sale but, the borrower would need to be in imminent danger of default.The lender, upon request by the borrower, must provide the borrower with any and all requirements for alternatives to foreclosure and give them 30 days to respond and meet the requirements of the lender.

It's dangerous to make tax decisions based on one podcast without a solid foundation of understanding real estate taxation. 

In such cases, the local fire marshalls may have authority. some jurisidictions require tanks to be cleaned out and filled with sand or other inert substance. some require sampling. you can check with the local fire marshall without identifying the house.Again, you should find out why the tank is not used. if its because the seller no longer occupies the house, then the tank may still be able to be used. sometimes, owners decide to put a tank in the basement. you should find out if it is truly an abandoned tank or just temporarily inactive because the seller is not using the house....  

Are there any dangers or responsibility from a landlord perspective? 

If you delead, and maintain the standard, you will be in the clear.Here's the law (emphasis added by me):460.100: Duty of Owner(s) of Residential Premises (B) Whenever any residential premises containing dangerous levels of lead in paint, plaster or other accessible structural material undergoes a change of ownership and as a result a child younger than six years old will become or will continue to be a resident therein, the new owner shall have 90 days after becoming the owner to obtain a Letter of Full Compliance or a Letter of Interim Control, except that if a child younger than six years old who is lead poisoned resides therein, the owner shall not be eligible for interim control, unless the Director grants a waiver pursuant to 105 CMR 460.100(A)(3).

Honestly, I find a lot of those guys to be more like flashy click-bait than actual substance. 

Each JV owes fiduciary duties to every other JV, so it is also dangerous in the extreme for novices.