I have been remodeling my bathroom in an old house with a 2 wire electrical system without conduit. It had a 2 prong outlet at the lower wall that I've replaced with a new standard 3 prong. Also I've installed a new 3 prong GFCE outlet for use at the sink - splicing it to the wiring that traverses between two old light fixture boxes where the old medicine cabinet was and am keeping for the lighting in the room. I am determined to ground all those properly, but without conduit to feed wires through, I am challenged to ground these without being somewhat creative. Also there are ground wires leading out from the light boxes themselves.
I have wired the GCFI at the lighting circuit using the input and output features on the back of the outlet, so that there are a total of 4 wires along with the ground, so two wires are going from the back of the outlet to the second light, and two wires leading from the first light.
I am determined to ground the electrical items for the bathroom, despite learning that GCFI outlets are okay to leave ungrounded. Further, having a ground to the lights seems like a good idea anyway and want to use the ground wires from the light boxes. I have tested the outlets using an outlet checker, temporarily using the cold water pipe as a ground, and the lights indicate "correct" for the power and the ground.
I am not intent upon using the water pipe, but only to test what I have already done.
Can all those items be grounded with to a single common ground wire - considering that the lower wall outlet is possibly on a different circuit from the lights and the new GCFI? Does the ground for those items have to return to the common ground at the electrical box? Can a separate grounding rod be used if more convenient? Is it okay that I've spliced the GCFI outlet in-between the two light boxes the way I described? Can I run the ground wire(s) outside using some sort of weatherproof wiring ( if such wiring exists ) stapled to the exterior of the house?
Is my determination to ground items in the bathroom warranted? Should I consider simply relying on the safety features of the GCFI outlet and then install another GCFI at the lower wall - without grounding anything? Would leaving the light boxes ungrounded despite noticing ground wires be okay? Is the reworking of the bathroom this way making the old wires leading into the bathroom subject to replacement.. or are they okay as they are?
The house does have a breaker box at the back exterior.
Please word answers simply as possible without jargon like "daisy chaining" as I become confused easily sorting out condensed phrasing and concepts familiar to professionals.