Well, if you aren't sure what to do, then I guess you don't have a compelling reason to stray from the setup that is proven and more simple. Since the zenmuse needs 4s minimum and the power consumption is rated at 200-400ma which is equivalent to a string of led lights or a fpv transmitter. This is very low. In addition, a second pack requires another battery has to be charged, mounted and monitored, and since the flight controller absolutely must communicate with the Zenmuse in order to function, you are guaranteed to always have power to both with a single pack. The extra weight of a second pack will likely cost you more flight time than the consumption of the gimbal. If you the gimbal needs to be mounted and removed from the multi rotor on a constant basis, consider mounting the GCU to the hex instead. This will allow all your electronics to be neatly organized in one place, and allows the zen to be removed with a single connection. Having the GCU on the gimbal means a latching can bus cable must be detached, and these are very fragile. Hope this helps.
Also, Im not sure what your flying this with, but I can get 14 minutes flight time on my Octo with this setup off of 15,000 mah and nearly 20 minutes with more battery capacity. If your going to add battery, why not add it to the main? Your Led lights also won't run off 4s and 3s won't run the gimbal. In scenarios where LED lights and FPV tx cannot handle 6s, I recommend a 12v regulator. Less batteries= less hassle.