As far as the other property, my ultimate desire is to build a duplex for rent. 

I would spend some more time on building capital so you can make sure you have money for reserves if things go wrong. 

After researching online I found landlord responsibility under California Civil Code section 1941 described as followsClean and sanitary buildings, grounds and appurtenances (for example, a garden or adetached garage) which are free from debris, filth, rubbish, garbage, rodents andvermin. 

It started out as a verbal agreement because time was a factor.

that is not how cash flow works.it's also going to be challenging to get lending on properties priced that low - it may be difficult to get standard conventional financing.and finally, the lowest prices are going to be in the most challenging neighborhoods... which will come with additional challenges.some suggestionscan you spend some time researching neighborhoods more broadly, going to REIA meetings, and building a network?  

What factors are best to look at to determine if a property will appreciate the most? 

The more relationships and marketing channels you build will only benefit you in the long run.

The Columbus macroeconomics is booming due to many companies building out here like Intel, Meta, Google, Amazon, etc., and there is continuous population and job growth!

Loans can be as low as $50K or as high as $300K depending on whatever factors they are looking at in your financial profile.  

Quote from @Richie Linnon: I don't recommend small increases over a long period of time because it increases the chance of mistakes, it may still build animosity with the tenant, and the tenant may eventually reach a point where he can no longer afford the increases and he will leave.