Pins 4 - 5 and 7 - 8 are not used for carrying network signals. They may be used for other purposes.
Cat 5, Cat 5e
Yes
Copper.
RJ-45
An RJ45 connector has 8 conductors. it has the naming convention of 8P8C (8positions 8conductors).
Cat 5E
Cat 5E
Cat 5E or Cat5
Cat 5, Cat 5e, Cat 6, Cat7
Ethernet cable of cat 5e or cat 6 connected to modem or router
The bulk cat 5e is a long line of professional cable used to wire a home or office space. They also come in a variety of types from solid or stranded to plenum, each of which depends on the condition in which the cable will be used whether it be immobile, constantly moving or flame resistant.
If you can use fiber optics. If not try to use CAT-5e at least, CAT-6 is recommended.