You just need to connect what you are using. You are only using two white coax cables, one for G3100 and one for basement MoCA adapter. Theoretically, you can just connect them using a coax coupler (1 IN, 1 OUT). Since ECB5240M adapter comes with a 2-way splitter in the box, if you decide to purchase from Verizon, there is not need to buy extra coax couplers or a 4-way splitter. Technically, to connect all 4 coax wires, a 3-way splitter is fine (1 IN, 3 OUT). On my diagram, I have a 6-way splitter (1 IN, 6 OUT). All six ports on the front (2 on the top row, 4 on the bottom row) are OUT. There is a side port that is kind of hard to see behind the top row. That is the IN. All MoCA devices are on OUT. For IN port, I am using it as a ground wire (using a groundable coupler to conduct the shielding). Again, for MoCA signal, it does not matter you connect the device on IN or OUT. If it makes you happy, you can connect the coax from G3100 to IN, and basement coax to one of the OUT. Leave the other unused OUT port.
That black wire coming from the Orange Tube, is it a coax wire? Since your Verizon fiber comes from the same tube, I am assuming that is reserved for cable Internet Service from the street, which you are not subscribing. Even if you want TV service later, you won't connect that black wire, the TV coax comes from the ONT.