Steve Ontiveros wrote: 1. Are there building codes that must be adhered to when building your dwelling?
Short answer is yes. Long answer is it depends on the county, the more rural the county the more likely building codes are unenforced or nonexistent.
Steve Ontiveros wrote: 2. In terms of sanitation, am I free to build a septic system/leach field at my discretion?
No, human waste disposal is something almost every county enforces. I'm sure there are exceptions, but I don't know them specifically.