By keeping each "type" in its own LLC, you compartmentalize your exposure. 

The air source is probably an issue, the room in which the furnaces are installed is really just a hallway, but we decided there were too many other flubs that need fixing, and it didn’t look like all the wood steps & decks were properly weatherproofed, esp on south exposure.

We have insurance, but last time I checked, insurance companies don't like to pay claims.Since we don't operate property management or rehabbing businesses, our exposure is minimal, but I still want to discourage attacks.Seems like having assets in your personal name is just asking for trouble. 

Like I wouldn't have an LLC that owns both an office building and a SFR.You may want to speak with an attorney on the best route for entities depending on your risk exposure and risk appetite.Like maybe you have assets inside of an LLC until it hits $500,000 and then you create a new LLC.

Both state that parents nowadays are actually more interested in renting or even flat out buying condo units to keep their kids safe from reckless teenagers or limit their exposure so that when they come home their chances of accidentally sniping off grandpa are lowered.This makes me wonder if these types of properties are still worth chasing.

I'm looking at a multifamily 4 unit with a "bonus" basement unit in Illinois. 

Buy it based on the current number of units, and if you can add one more in the basement then consider it a bonus, but don't base your offer/purchase price on the assumption you'll be able to do so.

The bonus deprecation allowed by the 2017 tax act has opened up many opportunities for investors to do better without a 1031 exchange than with one.

My dad has a couple commercial and residential properties I manage for him, but I wanted to get more exposure and experience than I am currently getting.

Another option in place of the transaction fee is adding a bonus on your end when a transaction does go through.