Driving in December from Hakone to Takayama

Hi!!

We are planning a trip in the beginning of December. I am trying to figure out the safest and most efficient way to travel from Hakone to Magome/Tsumago to Takayama and end up in Kyoto. From Kyoto we'll make our way to Wakayama to do a day or 2 of the Kumano Kodo trail.

I was thinking about taking the train from Hakone to Magome, hiking from Magome > Tsumago, sleeping in Tsumago. Then picking up a car from Magome (Is that even possible?) and driving from Magome to Takayama. I see the bus closes on November 30th from Magome to Takayama..does this mean driving is not advised?

If not driving this route, what would everyone suggest? Train?

If train, do we need to purchase ahead of time? If so, where can we purchase?

Thanks so much!!!

Then picking up a car from Magome (Is that even possible?)

There are a few outlets at nearby Nakatsugawa Station. It does not sound like a bad idea. The later in December, the greater is the chance of encountering snow and ice. If you don't know how to drive in winter conditions, I recommend to use public transportation for this leg, as well:
https://www.japan-guide.com/e/e6079.html?aFROM=5900_6075

I see the bus closes on November 30th from Magome to Takayama

There is no suach bus in 2023. You must be looking at out-of-date information. In past years, there was such a bus, but it would only operate outside of winter because the demand would drop during the winter.

If train, do we need to purchase ahead of time? If so, where can we purchase?

Almost all trains have unreserved seats, so you can ride them without prior reservations:
https://www.japan-guide.com/e/e2016.html