We have a little trade going where I can help them out on work if they help me out on property buying/selling side.

Although they really believe this is an even trade, I question what a new REI has to bring to the table of value...and this isn't meant as a criticism...just a point of fact.There is a reason why there are so many that are not successful in this career (and others as well). 

If the other unit is unaffected and inhabitable, a lender may underwrite ...That said, if you can swing it, you ,may be better off buying cash (using that as leverage to drive the price even lower), affect the repairs to the damaged unit, then finance once complete.

Income - 50% of income gives you your NOI and from there if you know your area then you should know at what CAP rate comparable properties are trading at.

From the 1098 instructions:"File this form if you are engaged in a trade or business and, in the course of such trade or business, you receive from an individual $600 or more of mortgage interest...

I thought all you needed was a pile of cash and the ability to swing a hammer!

most tub manufacturer have local guys that can do a perfect repair. you would be surprised how often new tubs are damaged by other trades. the repair guy will often have 20-30 jobs in one subdivision.

I'm an experienced visual designer with a background in marketing, so perhaps we can trade advice for services down the road if that's interesting to you.

If you’re comfortable with massive swings of wealth, then don’t diversify.

It's a trade off, if they would like to do it that way, they just have to put more time into it.