Grew up in Lakewood long before it incorporated.  

Is there anything I need to incorporate into my numbers?

Incorporating custom esign capability for addendums would go a long way to making this a powerful tool.

I am a partner with cousins, this is an inherited property.I have a decent handle on the property value.How do I incorporate the value of rental income into the selling price?

Adalanto, CA is a prime example, but it is a separately incorporated city which set up an area specifically for this.  

They don't have an app for iOS or Android yet but, I know that they're working on it.I love that it's free but, if they did charge a small fee (emphasizing small) I'd still use it and incorporate the extra cost into the rent.

Owner occupant loans have ways of including/incorporating that "boarder income," but alas investment property loans do not.

I can email you an APOD/proforma spreadsheet that I use that incorporates CapEx, and all other expenses including property management and vacancy etc., debt service, and tax deductions, and gives you the COCR, cap rate (which I know isn't supposed to apply to duplexes but I like to know it for comparison's sake), and net annual income, along with projected appreciation value at different rates over time.Right now, I personally like to see at least 12% COC and a cap rate over 7, after rehab.  

Your options are to legalize the inlaw (making it a legal 2 unit bldg and subject to RC) or incorporate the downstairs into the main house, increasing its size, while keeping it a true SFH.

The rehabber is incorporated locally near the location of the properties.