A TrueCrypt Keyfile generator generates a keyfile of size 64 bytes. Can I change the size to become like 100 bytes by adding some more random data to it? Also, Is it good idea to store it on Online HDD on some server for backup?
I wouldn't recommend saving it just on a server for backup. If something happens to the key while you don't have access to the server then you have no way to decrypt your files. Personally I save the key on a USB thumb drive so it is always readily available.