Be aware that in the current scripting language the only way to get file content is to read all of it into a variable at once. Variables are currently limited to 4096 bytes at most. Assuming that on average the decimal representation of an octet will take 2 characters, each IP address would be (2 * 4) + 3 + 1 = 12 bytes (4 octets of 2 characters each, 3 dots and a carriage return), so that would give you 341 IP addresses per file. You'll like have to split your list over several files.
If you search the forums, there's many posts in the scripting section that deal with reading in lists from files and processing them. You can probably adjust one of them together with the manual section on scripting you can find on the wiki.