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Wait till you are past the threat of freezing weather to plant it.

https://www.gardeningknowhow.com/ornamental/flowers/roses/training-climbing-rose-plants.htm

Yes. You can cut it back to about 6 inches and it should send up new shoots. You also could try rooting some of the top growth that is cut off and make new plants for yourself or others. Here is more:

https://www.gardeningknowhow.com/ornamental/flowers/roses/training-climbing-rose-plants.htm

https://www.gardeningknowhow.com/ornamental/flowers/roses/pruning-climbing-roses.htm

https://www.gardeningknowhow.com/ornamental/flowers/roses/roses-from-cuttings.htm

Sure! This article will go over how and when to prune:

https://www.gardeningknowhow.com/ornamental/flowers/roses/pruning-climbing-roses.htm

Give them another chance! Clean up any fallen leaves beneath them in case a fungal infection caused the leaf drop. That will help prevent the same thing next year. You may have a single blooming climbing rose bush. They are pruned after they bloom if needed. Here is how and when to prune:
https://www.gardeningknowhow.com/ornamental/flowers/roses/pruning-climbing-roses.htm

ZD is susceptible to black spot. Counter measures to consider: Such a heavily blighted black spot diseased plant is going to be very stressed, may lose all/most foliage and may not produce flowers or may produce fewer. Attempt to reduce the humid environmental conditions that promote germination of black spot. Try opening the rose for better air movement and more sunlight (move the pot?) as these steps will not be beneficial for spore germination. Never water the leaves; only water the soil. Begin a fungicide spray program early; spray the plant as soon as brand new leaves first start to form in late winter or spring. Repeat as recommended in the instructions. Consider spraying with a propaconizole-based fungicide (commercial names Banner Maxx, Honor Guard, Fertilome Systemic Fungicide, etc.) about every 2 weeks in unison with a potassium bicarbonate-based fungicide called Greencure every three weeks for several years until there is some degree of control. Since you do not have a dormant season per se, consider continuing the fungicide applications in winter (maybe only temporarily stop around in late Jan-Feb if there is no active growth then). Pick up/discard infected leaves immediately, as opposed to letting them drop and then picking them up. Replace the spore laden, old mulch with new mulch. You can either move the pot or transplanting into the garden if the new location will improve airflow and increase direct sunlight. If transplanting into the garden, ensure the plant has fortuneana rootstock. Assume the spores are almost everywhere.