Theoretical limit?
Take the entirety of mankind in the BT universe and plan them as crew. That results in about 3,663 million stations combining a mass of 9,157 teratons. Now, installing a NCSS in each of those stations makes them able to send commands once to 87.9 billion SRCS-equipped stations every turn, thus extending that multifold. Provided the SRCS stations require a software update at least once every millenium - as the scoping span of Battletech - we can therefore deduce about 277.3 quintillion stations thus sharing in our network massing up to about 693 million exatons.
For plasticity, if we wanted to install this in the solar system we'd basically convert all planetary masses except Jupiter into such a station complex. Built as a Niven ring at 1 AU distance this ring would have - at a thickness of 1 km and the density of Earth - a width of 1,150 km, providing a population density upon it of 1.85 people per square kilometer area or about one-eighth what it is today on the planet.