Hi there,
The Fuji Q-Pack ticket includes a Fuji-Q Highland one day pass and round trip Express Bus ticket from Shinjuku to Fuji Q Highland. Fore more details, please see the link below.
https://www.fujiq.jp/en/qpack/
In your case, I would suggest booking a round trip ticket from Shinjuku to Fuji Q Highland on line and then buy the Q-pack ticket when you purchase the bus ticket at the ticket counter in Shinjuku.
http://highway-buses.jp/fuji/
If you would like to go to Kawaguchiko, you can take a local bus from Fuji Q Highland withour any reservations.
It takes about 10 minutes from Fuji Q Highland to Kawaguchiko.
I think this is the most reasonable way to enjoy the area.
I hope this information is useful for you.
Have a nice trip in Japan!