Hi there,
A 7 day rail pass starts to become cost effective if you spend over ¥28,300 on JR tickets. A 14 day pass becomes economical if you spend over ¥45,100 on JR tickets. Lets take a look at the legs you mention to see if you'll be able to save with a rail pass:
- Narita airport terminal 1 > Tachikawa: ¥3550, (119mins, 116km)
- Tachikawa > Kyoto: ¥13110, (214mins, 531km)
- Kyoto > Tokyo: ¥13220, (161mins, 513km)
- Tokyo > Odawara: ¥3640, (35mins, 83km)
- Odawara > Tokyo: ¥1450, (36mins, 83km)
- Tokyo > Narita airport terminal 1: ¥2940, (58mins, 79km)
TOTAL: ¥37910 for 6 legs
As you can see it will not be economical to use a 14 day rail pass for your trip as the pass cost is more than the ticket costs of your intended travel. However, if you manage to fit all your travel within 7 days, you'd certainly make good savings with a 7 day japan rail pass . Taking out one of the narita legs would bring your ticket spend to ¥34,970. With a 7 day pass you'd save ¥6670 over standard tickets. Of course, this depends on if your plans are flexible enough for this.
I'm afraid upgrades to first class by paying the difference are not possible with the Japan Rail Pass. However, you can use the Rail Pass to cover the basic fare and then pay the full Green Car seat fee if you would like. In this case, the trip to Kyoto in Green Car will be ¥9,880 one way with a 7 day standard class rail pass (normal green car price is ¥17,860).
Hope this helps!