How do I find out what I need to overwinter inside and what can be left outside?
Ferns (Kimberly and Boston)
Air Plane plant
I'm not sure about the Kimberly fern, but Coreposis is the only thing that can take a freeze, the rest probably cannot.
Begonias, and pelargoniums (which a lot of us call geraniums) have no tolerance for frost or freezing, although I've found that well-sheltered common pelargoniums mostly do okay down to about 35*. You can lift, pot, and bring inside to overwinter; or take cuttings; or [pelargoniums] trim severely, then dig up with a chunk of soil and put into a paper bag and keep in a very cool, dark site like a basement. Mist the soil about once a month and then bring into warmth and light about a month before the last frost - add moisture, and they will be close to blooming by the time you can plant them back out.
Geraniums/cranesbill are mostly hardy for overwinter (give them a loose pine-needle mulch), but you need to know just which species in order to be sure.
Many ferns are winter-hardy, except for those that have been imported from the sub-tropics for indoor use. Again, you need to know just which ones you have. As far as I know: Kimberly is native to zones 10 and 11; Boston ferns are zones 9 - 11.