I would like to have lower monthly payments should I make a big lump sum payment towards my principals and ask my mortgage company to adjust it or refinance it or which one is the best ? 

Seems like it's in a lower end area so if it is filled you will have tenant issues and turnover cost.

Buyers that would buy if rates were 1% lower.

If I have lump-sum free cash, should I just apply it to my mortgage to recast so that my monthly goes lower?

This implies residential units can be built at lower costs and provide better return. 11) adding an ADU to SFH can make the SFH fall under rent control.

I have several clients who have invested in Vegas and had a lot of success but now they're focusing more in the southern/middle part of the country because the price points are lower and the laws are more landlord friendly.

Some of the costs quoted shock even seasoned flippers as they are lower than even material are in many markets. 

BoA is fine for this sort of setup.. but consider a local credit union in San Diego for lower fees and simpler sub-accounts from what I’ve heard.

I'd assume all vanities, lower cabinets, 3to 5ft of drywall and base will all need replacing. 

When you researched markets like Austin las Vegas Miami, those markets have higher land cost and are more cyclical in nature tend to have larger price swings compared to regions with lower land costs.