They are different things and do different jobs. A cable is a conductor to carry current, a conduit is the protection for the cable in which it is placed.
In conduit is way better option. Protects the cable from people digging around it. At least will hit conduit before hitting the wire. Also protects the cable from whatever is placed in the hold when backfilling
No, the electrical code requires that the mineral insulated cable be strapped at proper intervals and not be piggy backed on to other conduit structures.
The outer casing of an Ethernet cable does not have a UV rating and will deteriorate under the summer sun. Pull the cable into a conduit and if possible bury the conduit underground. This will give you a safe and secure link.
One can find information about conduit fittings from various sources. Some of those sources are Grainger, Home Depot, Prime Conduit, Steel Conduit and Lowes.
Generally cable - size depends on the load
For cable not in conduit and intended to be installed without conduit, such as NM cable, yes. You must provide some form of connector that will hold the cable in place. A clamp is not the only kind of connector that will do this but is the most common.
You should probably use electrical conduit approved for this purpose, and not hose - anything else is unsafe and will fail. To get the cable through the conduit: Find a styrofoam ball, ping-pong ball, or similar very lightweight ball just slightly smaller than the inside diameter of the conduit. Push the end of a piece of lightweight nylon twine (longer than your conduit) through the ball and tie it in a knot. On one end of the conduit, attach the hose of a shop-vac - and at the other end, drop in your ball. The vacuum will suck the ball and twine through the conduit. Retrieve the ball. Then use the twine to pull your line through the conduit (if small wire), or to pull a length of stronger rope or cable through before attaching it your wire.
Armored electrical cable contains insulated electrical service wires protected by a flexible steel covering. Metallic Conduit is a tube or pipe though which we lay electrical cable.(Most commonly lighting cables).
The advantage of using armoured cable over rigid conduit systems is the flexibility of the cable. There are some situations where conduit can not be bent into the shade needed to make a proper connection to a device. Because of the flexibility if the armoured cable it can be used instead to make a presentable looking job.