Now, the current owners spent 30K to finish the basement professionally within the last year.

Do we, for example, sell our current SFR and put all/most of the equity into a down payment on the duplex and have a lower monthly mortgage payment?

Our current apartment is too small for that. 

Currently I hold a few rental properties in California, but I am looking to expand out of state mainly because of the cost to acquire new properties in California has made it difficult to grow here.

You need a quality realtor that can advise you on current value and after repair value estimates.

Some title insurance policies require a current survey, but if this is a re-insurance policy (with the seller's title insurance company) then you saved yourself (potentially) a lot of money.

Gives really good insight as to what's currently going on and then apply it to your investing goals.

I’ve got two women in one unit I suspect are washing clothes and hang drying them as the washer is currently getting the majority of the money.

For travel medical professionals I will accept a copy of their fully executed contract in lieu of pay stubs because their prior pay stubs may be totally different than their current contracted rate. 

I currently have saved a lump sum of money...