So an infinitely long rod would have both infinite qualities while also having form.
Then this compromises your definition of form.
Given general relativity the rod would inevitably curve around and join its beginning forming a ring, in order to be truly infinite as the rod were being measured the "person" taking the measurement would become locked in a pattern of infinite revolutions around the ring and would never reach the end.
The above paragraph makes no sense.
There is a possible geometry of universes where rods can only do this, but given such universes, you cannot describe the rod as infinitely long. If it helps, go two dimensional and consider a geometry like the surface of a sphere similar in size to the earth. The longest possible line on this surface would be the size of its "equator", about 40,000 km. That would not be infinitely long.
Furthermore, that's a possible geometry, and it's not a consequence of GR that the universe has this geometry.
I can conceive of no other way in which a finite thing could also be an infinite thing.
An infinitely long rod is not a finite thing. It does has a finite measure in one dimension and an infinite measure in another.
It sounds like you're wanting to grant "form" to this object, but to
argue that form means it's finite, so you're trying to make it easy by slipping it into your definition. But per your definition, "form" is simply another way of saying "finite", nothing more.
I think you want to define form differently. From the way you're using it, "form" is something more along the lines of "state".
I agree about "nothing", it sounds odd, but I think it can exist as a concept.
But concepts are abstract things. To speak of "nothing" as if it were a thing is to commit a reification; to talk about its properties is to talk about it as a thing.
Think of it this way. If something does not emit a lot of light, we'll say that it's black. A lump of charcoal, for example, does not emit a lot of light--so it's black. Would you say that nothingness, since it does not emit a lot of light, is black?
We can treat nothingness as a concept. But we can't treat it as a thing.
ETA:
It seems you're establishing a pattern here--you're committing the same kind of error twice.
In your definition of form, you're imagining what "must be so", and are using it to formulate (no pun intended) your definition. In other places, you're saying that nothingness is the "most logical" state of affairs, but you have no legitimate argument that nothingness is the "default" (why wouldn't existence be the default? It's what we actually see!)
In both cases, you're presuming that you can somehow argue up properties of actual entities in universes. But that is the problem--you cannot. You can't use pure logic to figure out what Nature is like; she is her own entity and not obliged to follow your notions. She is what she is, and she does what she does. The only way to figure out what she is is to ask her; and the only way to figure out what she does is to play with her.
Don't try to speculate her into a box--it doesn't work. Just go talk to her! Don't be shy.