I will attempt to answer only item (4).... 106th Avenue...

Actually, this is all that remains of the Southern Pacific's "Stonehurst Branch" that veered off of the SP out in East Oakland, and ran up the center of "105th Avenue", then crossed over a wig-wag protected major arterial (East 14th Street), thence alongside of and to the rear of the old GM-Chevrolet TRUCK PLANT. The outlet from the rear of the Chevy Yard ran on private right-of-way between adjoining homes, across Sunnyside Street and up to Bancroft Avenue..

Upm until March-1941, the tracks tied into the SP/IER electric commute tracks of the Seventh Street line. The double-track main ran down the unfinished portions of Bancroft to 73rd Avenue in East Oakland. At 73rd Avenue, tracks split into a very large freight yard in a residential area, that was used for switching for the big GM-Chevrolet AUTO Plant, which was located where the large EASTMONT MALL is now...

The double-track SP/IER mainline continued WEST onto BOND Street and on down to 46th Avenue & East 14th Street where the tracks crossed East 14th St again and arrived at the MELROSE Station.
From there the tracks crossed East 12th Street and San Leandro Street and joined back into the 4-track SP mainline, just South of HIGH Street.

At one time, a steam train could head South on the SP mainline from HIGH Street-- branch off onto the Stonehurst Branch, head back West/North on the IER/Chevy industrial lead, and end up right back where it started from...

Hope this helps out your curiosity.

Henry.