Bonding new communications system to home grounding system
The water main is a grounding electrode, but not a grounding electrode conductor
You are correct that a metal water service line is considered a primary grounding electrode when present; however, not the least due to the potential for the utility to replace said metal water service line with a nonconductive, non-grounding plastic water service line, the NEC requires a supplemental &quot;made electrode&quot;, usually a pair of ground rods 8' long and 6-8' minimum apart, when the primary electrode is a water service line.  For these rods, NEC 250.66(A) lets you use 6AWG copper to tie them back to the main grounding electrode conductor.
However, you must tie those rods back to the grounding electrode conductor in addition to tying the lightning arrestor grounding wire to said ground rods.  (This is required by NEC 250.50 and 800.100(B)(2) or 800.100(D).)  Furthermore, the reason you see the Grounding Electrode Conductor tied to the grounding electrode at the service entrance point is because NEC 250.68(C)(1) requires that connection to be made within 5' of where the water service enters the house.  (This requirement exists so that a plumber doesn't accidentally leave your house afloat in the electrical sense of the term.)
So, I would use plan #3, but modified with the addition of a second rod, and more importantly modified to use either a split-bolt or a T-tap connector (Ilsco GTT-2-2 or equivalent) to connect the bonding jumper to the GEC directly without having to sever the latter.  You can connect the lightning arrester's bonding wire the same way for now; generally speaking, though, you'll want to put in an Intersystem Bonding Termination device at the main panel if at all possible, as that provides a central place for future communications grounding wires to land.