Universal Control has no dependency on Studio One and vice versa. You can upgrade to Studio One 4 without having to worry about the version of UC that you're running.
To answer your second question:
UC 1.7.6 was the last and most recent release for the Classic Mixer series with 1394 including the SL1642, SL2442 and SL1602. We updated UC Classic recently to accommodate increased security requirements from Windows 10 and Mac OS 10.13.x operating systems.
The SL1602 may be the only exception as the 1394 version uses UC 1.7.6 and the USB version uses the newer UC 2.7 or newer.