On my duplex, the water is not split (electric and gas are separately metered.)

Origination charge being an example, but 1% on one property at $500k versus 1% on two properties at $250k/each...You still need separate appraisals, title work, filing fees (state/county/city) so trying to find a lender to bundle properties into a single loan likely won't fare you any better than just finding a good lender.

Considering you have all your rentails in the same area, are they considered one business or have to be considered for tax purpose separate.  

We bought a 117 year old duplex with a separate garage with apartment.

So if I have few properties shall I put each of them as separate LLC or put all my assets into one LLC?

We're planning to create a separate basement unit apartment and do some other updates.  

Its a 2/1 building in the front(That I would occupy), and (2) 1/1s in a separate duplex behind(That I would AirBnB).  

On the other hand, having 3-4 separate leases can help you should one person decide to default on the rent.

The umbrella coverage is also more dummy proof than an LLC which has various conditions necessary to provide the protection you desire (notably separation of funds which is not always easy). 

I'm more used to marketing as a Realtor, which is much easier but it's hard to separate the two.