As it is a normal priority package, we'll leave it as optional. Line 4 is the name and email address of the maintainer. Line 7 is the name of the binary package. Line 8 describes the CPU architecture the binary package can be compiled for. Line 9 shows one of the most powerful features of the Debian packaging system.
Packages can relate to each other in various ways.
Dpkg and APT should let you do it, though. Use this for packages that are not strictly necessary but are typically used with your program. Dpkg and APT shouldn't care much. Use this for packages which will work nicely with your program but are not at all necessary. The package will not be installed unless the packages it pre-depends on are installed and correctly configured .