In addition to the local REIA's, check into local real estate Meetup groups (Meetup.com) and there's also area-specific Facebook groups.

Especially if you have mature trees on the property, you'd want to inspect lines that were that age if you were keeping the property.If sewer line problems were a common occurrence in the neighborhood and having had them checked could be used as a selling feature, great.In other words, no, don't do it.

I want to add it to our rental portfolio.

So VRBO does my calendar, and mentions additional amenities provided as well.You can get an idea by looking on line and looking at properties to see what they are charging, how many days they are vacant and see if you can calculate how much you need during the off period.

Late last year we moved into a new duplex and kept the old one, and now rent out both sides, in addition to the other side of our current one.

Leave rooms unfurnished, supply basic (kijiji quality) furniture in the common rooms?

You simply have to know what you are doing, which means knowing your values and any potential additional liens you may inherit....code violations, past hoa dues, unpaid utility bills, etc.  

I know just from looking down that avenue myself, I've noticed that multi-families are not as common closer to center city.

I just found out another person is living on the property without my knowledge... I confronted the tenants and they said they like to add the new person on the lease. My question is:1. Do I have them all start signing...

In your area those may be very common.