Ya, I think just skip Odawara and concentrate on Hakone la.
Yes, if you have the Hakone pass, just top up 1090 yen (one way) if you are boarding from Shinjuku.
Romance car top up can be done without the Hakone pass too.
Refer to this website:
https://www.odakyu.jp/english/romancecar/surcharges/
I most likely will need that freepass since there are trains and buses to take from hakone-yumoto to attractions.