How much science do you like in your D&D?
Depends very much what you mean by 'science'. Science is an investigative tool for figuring out how the world works (make accurate predictions on how it will behave) based on empirical evidence.
The success of what we call 'science' depends on the world behaving according to certain rules which science assumes to be true - results are repeatable, the laws of the universe generally don't change with respect to time and space, the universe is made up of a finite number of things with a finite number of common properties which are operated on by a finite number of universal laws or forces external to those things. It's easy to imagine a universe in which 'science' isn't possible and it's an open question of science whether its assumptions hold true enough to explain all that can be observed. Currently science is at a bit of an impasse in certain areas - quantum effects don't appear to be repeatable and so are described probabilistically, dark energy opens up the possibility that the laws of the universe aren't universal, string theory seems to offer an infinite number of competing solutions, and of course there is the problem of explaining things beyond a singularity such as 'what happened before the big bang'. All of this may eventually get ironed out by better observations and theories, but the point is we can imagine a universe where each particle had its own behavior uniquely stamped on it, and nothing could be known by a finite being because understanding of the next state of the system required fully understanding all the states of the objects in it. In other words, we could imagine a universe where everything was a "three body problem" and no experiment was repeatable. In that universe, there is no 'science' in any sense of the word.
However, and probably fortunately for our sanity, the D&D universe is known to be nothing like that. Not only does it superficially resemble this universe in many generalities, but magic can be performed in the D&D universe with the precision of science. Or, to put it another way, I prefer my D&D universe to have magic as science. That is to say, the wizard of my D&D universe doesn't (or at least needn't) practice occult arts, but is a natural philosopher. Wizards are scholars and not occult priests. They may in fact investigate things far beyond themselves and meddle in powers beyond their comprehension, but only in the same sense that a scientist in this world might or the mad scientist of fiction generally does.
1. Do your monsters have *sigh* Lighting Blood, and are your snakes poisonous, rather than venomous?
I'm not sure I understand the question, but for the sake of being understood I prefer to use terms accurately rather than colloquially.
2. Is magic a kind of science?
Yes. It's the science of the imagined world, or at least the manipulation of it.
Is magic more than just the manipulation of particles through the generation of electric potential within the brain that couples with a force known as the Weave to produce effects on 3d-dimensional structures?
Well, some of your terms are wrong for my imagined world, but that's the general gist of it. Magic takes advantage of the fact that the boundaries between the areas known as the planes are porous and thinner than might be expected. So there is a great deal of available energy to use if you know how to crank the handle and open the window.
3. Are your worlds planets?
Not in any sense that the inhabitants of the world would understand. It's a ball of rock whose inhabitants creep around the outer surface hanging in a void. We'd look at it and think, "Planet", but the inhabitants would look at it and go, "That is The World." The planets are moving stars that are not in fact balls of rock.
Do they exist in solar systems with correct mass to radius, logical core composition, rational positioning, and mathematically accurate orbits?
No to all of that. The world exists in a void that is part of a higher dimensional structure, and which is bounded by a veil through which you can pass to the still larger void of the Astral Plane (which can also be entered at any point on the material world). The created free peoples live only in the lower dimensions of this structure and are generally unaware of what is transpiring in higher dimensions. The world however extends rather solidly into all the higher dimensions. This for example means that the ethereal plane is nothing like what you'd expect from normal D&D, and ghosts cannot normally go through walls. (If a ghost is observed going through a wall, it's an ethereal anomaly resulting from the ghost maintaining local ethereal space in a state close to what it resembled when the ghost died. That is, a ghost can only pass through a wall if a wall was not present at the time the person died. A ghost can however usually pass right through a door because of the time delay between the material and the ethereal aligning. However a door that has been shut for ages is effectively a wall on the ethereal plane as well. The same is true of a spell caster that goes ethereal.)
4. How do the planes exist? Are they separate from normal reality? How is this so?
They are normal reality. Most beings however are limited in their ability to understand the higher reality either through lack of the right organs of perception or lack of sufficient mental ability to comprehend what they perceive. For example, an Outsider will certainly affirm that any mortal on the Astral Plane is perceiving things only according to their conventional understanding and not able to see things as they actually are. Further, they will explain that it is impossible for the mortal to actually imagine much less perceive the actual reality of the Astral Plane. Even the immortal Fey can't really do it, they are just far more tolerant of not understanding and far more open minded about their perceptions than mortals.
5. Is your table of elements expanded to include metallic elements like adamantium and mithral? If so, how? If not, have you made metals like beryllium adamantium? Do you not worry about it at all?
The full table of elements is: fire, iron, earth, water and various hybrid particles of those things in unstable states (para and quasi-elementals). Everything else is made by arranging those things in various forms. So for example, sodium is a molecule and not an element. Oxygen is not an element, it is a molecule. The same is true of metals like adamantium (also called 'True Iron') and mithral (or 'True Silver'). I don't generally get into the details of the imagined chemistry, but adamantium probably differs from iron in having no paraelemental particles in its lattice while also having a higher percentage of quasi-elemental mineral particles. The former means it's less inclined to decay and the latter means that it would tend to absorb or redirect energy, making it less breakable and also less malable. No real world chemistry is involved, so even if there is a such a thing as beryllium it wouldn't necessarily have any properties in common with what we call beryllium.