Here's our itinerary:
Dec 22: Haneda -> Kyoto
Dec 23: [Kyoto]
Dec 24: [Kyoto]
Dec 25: [Kyoto]
Dec 26: Kyoto - Koyasan
Dec 27: Koyasa - Osaka
Dec 28: [Osaka]
Dec 29: Osaka - FujiKawaguchiko
Dec 30: FujiKawaguchiko -> Tokyo
Dec 31: [Tokyo]
Jan 1: [Tokyo]
Jan 2: [Tokyo]
Jan 3: Narita -> Home
The 14 day pass covers all our days, but we do have plenty of days without day trips (in Kyoto specially) where we won't have use for it. My other thought was to use the 7 day pass activating it Dec 26 onwards.
When I priced it on Hyperdia, I'm finding it to be cheaper if we pay as we go.
If we do end up buying the JR Pass (either 7 or 14 day), are any day trips worthwhile to add to make it worthwhile? For example, how about Hiroshima/Miyajima on Dec 28? It feels like that might be tiring given all the travelling around then, but without it the JR Pass doesn't seem to add up.
I also considering getting a Kansai Thru Pass for our time in Kyoto/Osaka/Koyasan (and maybe add Nara to the mix), and then get a 'Suica' card when we land in Haneda for all other non-Shinkansen travel.