Pasting the error message and/or the stacktrace helps.
The just spawn it at -500 y.
You obviously do not have a very good grasp on computing logic if you cannot manage to get one element out of a collection.
You should learn more about the Java language and/or the Bukkit API before attempting to write a plugin.
Nobody is going to just hand you code. Look into the following classes: JarFile, JarEntry and URLClassLoader.
Store the last time they moved, and run a repeating task every second or so, checking all of the times. It's not that complicated.
Just use it figure out what NBT tags are edited...
Use a a simple socket?
I have no idea how to, but I know you can do it with NBT. Look at some of SethBling's MCEdit filters.
Why are you posting random code?
Either your plugin is has a memory leak, or it just uses a lot of memory.
You're not allocating adequate resources to the server.
Your plugin.yml is not formatted correctly.
Separate names with a comma.