I think it's worth easily $200k I owe $125k. my 4unit has separate utilities I only pay garbage.

If I should keep them separate, should that also be an LLC, S-Corp or something else?

Would you suggest separate bank accounts, I am not sure we need an LLC with this property at least not at first given that it is an ADU and we do not want to put our personal property into the LLC.As we are interested in getting more into real estate investing in the future i am using this property as a learning experience and a way to get all of our systems up and running.

You don't need a separate bank account for each property.

That is typically considered a separate fee from standard management services. 

Inherited a property (6 units - 3 separate buildings that consist of a triplex, duplex & SFH) a few months back and we’re currently renovating the property.

My understanding is that the deposits are still the tenents money and that that money is to be kept in a separate account and returned to the tenent at the end of their lease. 

House hacking can be a viable option granted you're willing to have a neighbor either in a separate room or duplex.

If a lot is zoned for a duplex, each unit can be sold separately correct?

Separately, I think that a 10-15% fee on top of the project is what's the norm for a project manager to assist with the work and deliver a completed unit.