|I recently bought 2 large Monrovia Bauer's Dracaena (I think|
|CORDYLINE 'Baueri' is hardy to about 20F. If your garden gets colder than that, allow the foliage to die down with the first frost, then mulch over the roots to keep them alive. Healthy new foliage will appear in the spring. If your garden remains warmer than that, simply cut off the old foliage as it yellows.
Yellowing splotches on new growth can indicate insect feeding. Carefully inspect the undersides of the leaves for sucking insects such as aphids, scales or mealybugs. Once you've discovered the culprit, you can treat with an insecticide (as directed on the label).
Normal rainfall won't bother your plant, as long as the soil is well draining. You're right, the foliage can be damaged if it whips around in the wind. You can build a temporary wind shelter for your plant or you can wait until spring and then remove any damaged foliage. Also in spring, feed your Cordyline with a diluted liquid fertilizer (I use Miracle-Gro at half-strength). Feeding should help your plant produce healthy new leaves.
Best wishes with your plant!