What you do with them depends on a few things: Do you want to keep the whole lot? Do you have space for them in the tank, or in another tank? Will your local aquatic store take the spare ones off your hands? (don't expect any money for them though) How would you feel about just leaving them and seeing how many survive? Some people don't like doing this, and some fish are more predatory of their fry than others. It might be that the weak ones get picked off and you are just left with the healthy ones.
If you want to keep them in the same tank then some java moss will give them a hiding place. Any kind of plant with small leaves will help them hide from the adults.
They can leave home as soon as they are big enough to tell that they are minnows! If they're going to a shop then they might have a minimum size in mind, you'd have to ask them though.
Finally, I need to see a picture of the cute fish babies for squeeing purposes.
Could be! They can spawn quite often. My goldfish used to do it every 10 days, the randy buggers.
Have you got a filter for the spare tank? Sponge filters are best for fry because there's no way for them to get sucked in. If you've got a normal filter then you can always slide a stocking over it to stop them getting trapped in there.