keep in mind these funding sources are just HML ers..

Yes there are pros and cons for sure and like any marketing channel, SEO takes work and investment to master, but it's among the best and most consistent lead sources for motivated sellers. 

-Do folks have ideas about the best ways to source (i.e. find an option seller) for such deals?

A lease should state the heat source and who is responsible for paying for the fuel.

Even with a wholesaler, if they know what they have they won't just turn it over for less.Hard to source these kinds of projects at the beginner level especially. 

Do you have any go-to strategies for sourcing these types of deals or for speeding up the analysis process?

Obviously, multifamily has so many more advantages than a Single family home, but can have more barriers to entry.I would start by learning the business, learning how to syndicate and use seller financing, and then focus on two things if you want to invest in multifamily: Sourcing capital and sourcing deals.More units allows you to hire staff and create some economies of scale.

So I am not sure whether I really need sources of passive income right now considering that I have a lot of energy that I can spend on investment strategies that require more efforts and energy.

It is just a different source of the  funds.  100% LTV implies no money from any other source. 

A potential trap people may fall into is that they will borrow to source a down payment, therefore ensure you check existing debts and cash flow carefully otherwise you might be in over your head.