Day trip from Gotemba

With about 6-7 hours or so of free time in Gotemba,
1) do you think if it is doable to make a day trip over to Kawaguchiko and back?
2) And with limited time available, from Kawaguchiko, do you suggest if it is still worthy to get the Fujigoko Enjoy ticket or just pay as you go on the bus?
3) Is it possible to find a car rental company in Gotemba (if there's any) and drive up to Kawaguchiko? Is it difficult to drive? Any toll charges?

Thanks

90 mins bus each way

1) do you think if it is doable to make a day trip over to Kawaguchiko and back?

Some buses make the bus in as little as 50 minutes:
https://www.japan-guide.com/bus/gotemba.html

That leaves you with around 4 hours around Kawaguchiko.

Doable: yes. Worth the effort: depends on the person.

2) And with limited time available, from Kawaguchiko, do you suggest if it is still worthy to get the Fujigoko Enjoy ticket or just pay as you go on the bus?

Not worth it. The ticket is only worth it if you make the round trip from Tokyo.

3) Is it possible to find a car rental company in Gotemba (if there's any) and drive up to Kawaguchiko? Is it difficult to drive? Any toll charges?

Yes, there are many outlets around Gotemba Station:
https://goo.gl/maps/PVYtKxFGvu8WVu7UA

It is relatively easy to drive, especially if you are used to driving on the left side of the road.

You have the option of using toll roads for part of the journey, whoch would save you maybe around 10-15 minutes versus taking toll-free roads.

Thank you Uji. Your information is very useful to my planning.

Thank you Uji. Your information is very useful to my planning.