The
first Baker party discovered placer gold around Eureka in 1861. Prospecting didn't really return in earnest until 1871, and it was not until 1873 when the Brunot Treaty was signed that things became "legal" in the San Juans.
Silverton's early history was not nearly as "wild and wooly" as you might imagine, particularly with any respect to how Hollywood romanticizes the "untamed" west. The legal system, including courts with judges and elections, very quickly appeared. As did a printing press.
I cannot locate the date of the first town survey, but suffice to say that by the end of 1875 over 100 buildings had been constructed and the town layout existed at least between 11th and 15th streets and Blair and Snowden streets.
It's a very dense, slow read but Allen Nossaman's "Many More Mountains" series is an immaculate history of Silverton and the region. I've only yet finished Volume I, but I suspect answers to most of your questions are buried somewhere in Nossaman's text.