1) Poisonous? I don't know, but the worms will be healthier in fresh bedding. You will find, though, that some of your worms will not migrate over. Given the choice, some of your worms will stay on the mostly completely composted side.

2) Can you do the back and forth thing? Yes. Until the bin is full? Well, I thought the idea of getting the worms to migrate was so that you can remove the VC from one side after the worms migrate over to the other side. If you do that, the bin won't get full. What I would suggest is to get another Rubbermaid bin, drill a lot of holes in the bottom, put a thinnish layer of bedding in it, then place it on top of the bin you already have. The worms will migrate up. Add bedding whenever you feed. When the upper bin starts to get full, the lower bin will be thoroughly composted. Harvest the lower bin, then place it on top with some fresh bedding.

3) As I understand it, as long as they don't dry out and are not exposed to sun light, the VC will store for a year or longer. They will need to breathe. Odds are that you will find some worms in the stored VC, but they will be small. Toss them into the active bin.

I do pretty much the same thing in my RubberMaid bin except it's divided in half with a wire baking rack mounted vertically in the middle of the bin and only one half is used at a time. It uses the "lateral migration" method of harvesting too.

Here is a link that might be useful: RubberMaid Bin

1) The thing that is bad for the worms is harder to explain than just saying it's toxic or poisonous to them, so people just say "toxic" "poison" and let that be all the explanation required.

Essentially, you're taking a large volume of stuff, adding water, and reducing it's size and evaporating that water until it's a very small volume of highly concentrated substance. This means that if the ingredients or water had a tiny amount of stuff that worms don't like, such as salt, the finished VC now has a much higher concentration of it.

In the wild, there generally isn't as much food in such a short amount of time as you will put into your bin, and the rain will rinse away built up salts or whatever else.

In an indoors bin, the general paradigm is to aim for zero liquid runoff. If it takes more than a moment to understand how that causes the compost to be harmful to the worms, just put a pan on the stove, crank the heat up, and keep adding a little water at a time to see all the stuff that was in that clean, clear water concentrate its self on the pan.

I don't really like the idea of indoor bins and keep mine outside. That gets me a much larger bin and so much less effort to keep it working. Also, I keep the concentrations in check by periodically over watering the bin. I have a liquid collection system that ends in a bucket that has an aquarium air stone in it. This liquid is mighty fine for my plants, and keeps the bin more natural and fresh (like an occasional rainstorm came to it).

2) That's fine, but keep in mind that the worms don't like to be disturbed. Try to resist digging around and exploring the bin too much.

3) Good dirt is mostly VC. Store VC how you would store dirt... or any way you think will keep all of it's magic unicorn rainbows in it. Just keep it cool and dry. The wetter it is, the more air it will need.

I'm working on a theory about storing VC. My theory is that if you are compelled to store it, then it is likely that your bin is too small. My reasoning is that if your bin is sufficiently large, you will be able to harvest the VC as needed. Likewise, if you seem to never have the stuff when you need it, your bin may be too large for you to be able to supply it with enough food.