the water won't affect the eggs and they still have plenty of time to hatch
Baby snails are almost transparent as are snail eggs. They can be brought in on plants or even in the water that you have brought fish home in.
maybe but no one can be certein
Yes or the snail will take in to muck backteria and die :)
It all depends on what you want. In other words, if they are fish eggs do you want more of the same fish that are in the tank - and the same for snail eggs. The kinds of fish you have will tell you about the eggs and where they are found. Sclares (angel fish) deposit their eggs on the glass or a leaf. Cichlids usually drop their eggs into the sand. Siamese fish blow elaborate "egg nests" made of bubbles. A small gel-like patch on the side of the tank is usually snail eggs - unless you have a large snail such as a Mystery Snail.
Once you have snails infesting your fish tank you will find it very difficult to get rid of them. They seem to live no matter how hard you try to kill them.
This is can be a hard process. You will need to remove the mother snail. Take the father snail and put him in a separate tank; he could eat the eggs when the are secluded in a smaller spot. Use a fish net to put the eggs with the mother. Be careful! Clean out the tank as quickly as possible. Then slowly do the same process. I recommend though that if you already haven't, move the father to a separate spot; I heard they can be like goldfish and eat their young.
No
Well it depends if you want them in there or not. It's your choice.
I have raised blue mystery snails for a few years and I have never seen one lay eggs when they were the only snail in the tank. I have seen egg clutches that didn't hatch, but I attribute that to an issue of the environment and not the fertility of the eggs.
Depending on the species, and how long ago they were laid before you notices, roughly two weeks from now they should hatch.
Yes water snail eggs float. they are small white eggs that are most the time attached to somthing like a plant (fake or real) or the glass of a tank just be careful it shoulnt be near the tank light. :)