Hi there,
First, the Hakone pass's price is 5,140 yen for adults, valid for 2 days.
And the pass offers you to get free rides from Shinjuku by local and express ( except Romance car) train to Hakone, and all transportation within Hakone area.
According to your plan, you seem to get to Kawaguchiko then back to Shinjuku.
There are 2 notes for you;
1)This pass allows you to take you to Gotenba station, but you need to pay fare from Gotenba to Kawaguchiko,
2)This pass offers you discount fare for highway bus, but it's only from Gotenba to Shinjuku so that you have to come back from Kawaguchiko on your day back to Shinjuku if you use the pass.
So if you want to take the highway bus from Kawaguchiko to Shinjuku, you can't get the discount offer and you need make another reservation for that.
I think if you get many of rides in Hokone area and if you don't mind your cost for the extra transortation fee for Gotenba <=> Kawaguchiko, this pass would be worth.
Here is the Hakone free pass's detail;
http://www.odakyu.jp/english/deels/freepass/hakone/
So here are my answers for your questions!
1.Yes, you can. You can get it either at the vending machine or Odakyu centre.
Also you can purchase your pass and Romance car ticket at the centre in the same time.
If you mean if you can book online or not, yes you can and credit card is acceptable from;
https://www.web-odakyu.com/e-romancecar/?STICKY=13744
2.As I mentioned above, you have to make booking without discount offer of the pass to get the bus from Kawaguchiko.
Here is the timetable and booking website of Fujikyu bus;
https://www.highwaybus.com/gp/foreign/frgSelectBordingDate
If you want to use your pass's discount offer for your bus on your way back, please get to Gotenba station on the day you will on board.
Gotenba => Shinjuku will cost you just only 870 yen.
I think if you really don't care to take Romance car, then you can get the highway bus from Shinjuku => Hakone with 870 yen ( normally cost you 1,580 yen for one way trip).
You can save your transportation costs, though it might be just a little bit...
Hope this can be your help and wishing you luck to have the chance to see awesome cherry blossoms!
