There are 7 of us, so just wonder if it is easier to take the taxi vs. waiting for the bus
Do you mean taking a Taxis from Tokyo to Kawaguchiko? If so, no way, it takes more than 100 km even from Shinjuku, and thus costs more than 30,000 yen for one Taxi. For 7 people, you need 3 Taxis, so it costs nearly 100,000 yen (=1 thousand USD).
If you take a highway bus from Shinjuku to Kawaguchiko, it costs only 1,750 yen per person (12,250 yen for 7 people). But, you should make a reservation in this site.
Sorry, now I understand you are thinking of taking a Taxi from Kawaguchiko to Fuji Festival, but I cannot understand what do you mean by Fuji Festival?
Anyway, even in Kawaguchiko, you should take a Retro Bus. Here are the timetable for the 3 Retro Bus: Green Line to Lake Saiko, Red Line in Lake Kawaguchiko, and Blue Line to Lake Motosuko.
In the Fuji Shibazakura season, there are busses running from Kawaguchiko Station to the venue.
Or do you mean Fujikawaguchiko Cherry Blossom Festival? Actually, there is no venue for this.
But, there are many Cherry Blossoms and they are nightly lighted up from sunset to 9 pm in the Northern Coast of Kawaguchiko from April 14 to 22 this year. So, take the Retro Bus Red Line from Kawaguchiko Station to the Northern Coast of Kawaguchiko.
We're going to be there around the same time as you and we plan to take the special Liner between Kawaguchiko station and Fuji Shibazakura. Takes about 30 minutes and runs every 30-45 minutes. You can get a combination return ticket+access to the site. Here are the details: http://www.shibazakura.jp/eng/access/