What you could do with your pots is just dig a trench and put the pots in and put soil around them--just like planting them, except without taking them out of the pot. The soil will help keep the roots warmer than they would be if exposed to the air. Then when you decide where you want them, dig up the pots and put them where you want them. Some of the roots might grow into the surrounding soil, but that's ok.

Mandevilla, you can cut it back. It will grow back next year. Don't overwater it in the house. It will be kind of dormant for the winter (but don't let it get bone dry, either).

Begonias, that kind of depends on the begonia. Some go dormant in the winter, some you can bring in the house, some it's just easier to toss and get new ones next year.

Amaryllis will produce new side bulbs. Here we just leave them in the ground year round and they form clumps and bloom in the spring. They are ok to about 40F. They go dormant in winter and bloom in early spring, and grow new leaves after that. You can bring it in the house, but if it goes dormant, don't worry, stop watering it and wait until springtime and the outdoors to start watering it again, It will bloom and then grow new leaves when it starts warming up again outside.

Caladiums should be dug and stored for the winter after the foliage dies back.

Here is a link that might be useful: Caladium Care

Begonias - Tuberous begonias are worth saving if you have a place to store the tubers properly. This explains how:Tuberous Begonia Page
If the begonias are cane type (e.g. Dragon's Wing begonia), it's worth taking some cuttings & growing them indoors. It's what I do with my more fancy begonias that I grow from year to year. Besides, they make beautiful houseplants indoors too!

Daylilies - Your daylilies will survive fine in pots even if there is a nastier cold snap. My zone is very similar to yours (even though I'm in Canada) & last winter, we broke previous records for cold with a prolonged cold snap. The daylilies I had in pots survived quite nicely with no harm at all. I was surprised myself.

Mandevilla - Like Hoovb said, cutting it back won't harm it at all. When you bring it into the house, if you keep it too warm & water it too much, it will try to put out new growth. But unless you can provide it with LOTS of bright light, the new growth will be weak. Try to keep it fairly dormant & place it where it won't get warm.

Amaryllis - It will NOT survive outside where you are & I'd suggest growing it as a bright ray of sunshine for winter. It's what I do with mine here. Once it warms up (flowering will be finished then), you can place it outside to build its strength up for flowering next winter. You need to do this so the leaves can store the food needed for blooming next year. And it will need a dormant period too.
Here's more to show you how:
Amaryllis: Year-Round Care

Creeping Ruellia - I've never grown these so can't comment but they're supposed to be winter hardy in your zone. Still, I like Hovvb's advice to put your pots into soil to keep them warmer. It's a common garden practise for winter for plants we haven't decided where to plant yet.