As a general rule, each entity that files a separate tax return (partnership, s-corp, c-corp, etc) will need its own QBO subscription.

The main reason/difference between this and the delivery of electrical energy is that the losses of transmission of electrical energy are generally less than 1-2% (that's why we use electrical transmission methods over long distances, generally speaking). 

That definitely won't help when it comes to trying to purchase a new property with a conventional investment loan in terms of DTI.But yes, in general with every property you purchase with a conventional loan, it makes it harder to purchase another property with a conventional loan given the DTI restraints UNLESS you exponentially increase your income (preferably W2).

When I have seen this done or done this for clients, the properties being crossed are generally refinanced into the same loan, replacing your first lien (blanket/portfolio loan).

House hacking is not dead, but in general, house hacking with a net positive is a lot harder to come by right now.

The CE Shop is a good overall resource for courses for pre-licensing, but there are a million of them and they all generally do the same thing.

Does anyone here invest on SFH, townhouses, or condos in Tri-state or the North-East in general? 

This type of loan is generally considered riskier for lenders, often resulting in higher interest rates.In summary, the key difference lies in the borrower's liability and the lender's recourse options in the event of default.

inheriting tenants - generally it's better to start with a vacant property, spruce it up, and do your own screening. 

YMMV, but generally speaking, the LTV for SFH rentals maxes out around 75% and MFH is 65%.