A: No. Pvc pipe is not flexible
A: The pipe must be supported with one-hole straps. It does not twist. But if not supported it will sag. It does have some give but it is designed to run straight along a wall or ceiling and is held in place with the one-hole straps.
A: I don’t know what code is in your area but if the wire is rated for outdoor use I do t see why you couldn’t use this for that purpose.
A: No, must not. Search homedepot for outdoor conduit pipe insteads
A: No, you can't do this. This type of PVC pipe is much too flexible, so your pole will droop to one side even without the weight of the weather station on top. Try shaking a single 10 foot length of PVC pipe while holding it from the middle: the two ends will whip up and down by several feet. Even a 1.5 inch diameter PVC pipe whips around a bit when carried. If you connect 4 or 5 sections of pipe together it will be exponentially worse. Remember that the weather station won't work properly unless it is level and solidly mounted I don't understand why you want to raise your weather station so high in the air. The instructions for mine simply told me to keep it 10 feet above the ground and away from buildings and tall trees, so I plugged a 15 foot telescoping steel pole into in a cast-iron umbrella stand sitting in the garden. If you are close to a building, you can mount a short pole onto the roof.
A: Not thick enough to keep up that high without stabilizing
A: I don't think so. This is PVC that uses fittings and PVC cement. Not aware of any other kinds of fittings that can be used with this pipe.