Your failed sewer is clearly not that.You discovered a material defect in the property and have an out if you want it.

If the tenant identifies an area of moisture that may be causing growth we immediately address the source of the moisture, replace and damage building material (usually dry wall) and or use mold cleaning solutions/mold blocking primers as required. good luck

I understand that at a minimum, I HAVE to register in CA since that's where the property is, but the lawyer is indicating that NV's a friendlier environment for Landlords so I should register in NV and just "do business" in CA.My questions are:  Is there a material benefit to registering in NV and then also CA? 

These are tough. 

Sure, it was tough juggling everything, but once you get going, you’ll figure out how to make it work.

They bring food and hats and other marketing materials.

What you may save in material you will make up for in engineering and architecture fees. 

Then I asked if I could just store some materials on the land. 

Whether or not there is a self-employment tax attached is based on whether or not you materially participate in this business.

If you have a more extensive full gut rehab you need drawings depicting the work to be performed and material specifications.