Yes but you should not make it less than 1.5 times your physical memory unless your physical memory is really high (like 12GB)
The sizing of a paging file is usually dependent on the amount of physical memory installed, which you do not indicate in your question. Maximums can be set according to the amount of disk space available and their placement. Sometimes you can set the maximum much higher than would be used by the operating system, leading to wasted allocation of disk space.
When a computer saves a file to disk, it looks for the first piece of unused space (not necessarily a space big enough to save the file !). On finding empty space, it attempts to save the whole file. If the space is too small, it saves as much of the file that will fit, then searches for some more space until it's saved the entire file. This creates fragments of the file on the disk, which are linked by a 'tag' so the computer knows where each part of the file is. Having to search for fragments of a file can make a computer seem slow, as it has to wait for the hardware to find the pieces of the file before it can do anything with it. A disk de-fragmenting program collects all the 'pieces' of each file, copies them to memory, erases them from the disk, then re-writes the whole file to disk in one single piece. Regular de-fragmenting speeds up the computer, by reducing the time it takes to find each file.
No. Such an operation would not make any sense. The Windows paging file is constantly changing size. Not to mention that the amount of free space would change as soon as you opened a single web page.
you're using virtual memory/a paging file
A cluster is the smallest unit of disk space that can be allocated to a file
From TechNet: Set the Same Initial and Maximum Size Setting the paging file's initial size and maximum size to the same value increases efficiency because the operating system does not need to expand the file during processing. Setting different values for initial and maximum size can contribute to disk fragmentation.
Disk space
Paging is a way for the operating system to load data from a storage device onto RAM. When there is insufficient amount of space in RAM and if a page file is enabled, it will swap data between RAM and the swap file (typically on a storage device).
Paging file is located in the root folder of the system drive.
df df - report file system disk space usage du du - estimate file space usage
Space. Speed - if the boot drive is slow and you have an alternate drive that is faster (don't want to reload windows) - a faster paging file will increase speed of Windows when you have a lot of applications running.
A dirty page is one that has been modified and does not exist in its current state in the paging file, so it has to be written out to replace the page in the disk.