first of all...which places do you intend to visit ?

second of all...what's your budget ?

with 8 pax...you will need a mini-van

This is still very broad. What are the places you plan to go?
Try checking out the attraction for the places and plan your itinerary. Once done, people here may give you suggestions if its feasible or not.
Then you may get suggestions to adjust on finer details.

Different people got different things they find attractive. Food and view, Temples and castles, hiking and chill, etc.
If we were to include all, nobody could explore in a short time(and enjoy it).

Not for me, and generally if you see no replies or lack of response to the specific question - likelihood is that no one has ever tried it/ used the service from the exact provider. In any case, check for reviews online and see if anyone encountered problems/ issues.

Maybe wanna check this out:
https://www.tripadvisor.com.my/ShowTopic-g2...tive-Japan.html

i have use tocoo before (car rental and Wifi) and yes they are reliable. Response from them are also very prompt.
You can try Rakuten for car rental, heard it is cheaper

bro let me know review when you're back, planning to rent one in July for Hokkaido

U only focus on few Kansai cities, public transport is better than self drive.......as parking fee at big cities liked Osaka, Kyoto is very high, sometimes hard to find parking at tourist spots.

Yes, Tocoo is trusted.

If you have someone elderly with you, who also has difficulty in walking, then yes I do agree on getting a car for her convenience. Just budget in advance for parking fees, toll, petrol, car rental etc. It would be too tiring for the elderly to take public transport.

no need to dilemma...you have to spend for your family comfort, nothing wrong in that

better to have a happy family during vacation rather than a unhappy one

I will recommend you to take taxi inside the cities such as Kyoto and Osaka.  The reasons are:
1.  The parking near tourist spot may far away from tourist spot, they still need to walk some distance.  If you use taxi, taxi may just drop u all in front of the tourist spot.  Your trip may just focus one or two tourist spots per day,  and you have 6 adults, the fare is divided and may cheaper than you rent a car.
2. Osaka is a big city, once your miss a junction, you may need to make a big round.......may waste your time.

I guess can apply to 6+2 or 8 adults as well.

I think they were just went for a short trip such as 2 days 1 night at Hakone.  Just need to bring a small back pack for one day stay.

Don't worry about your luggage. Bring 2 bags, the big one you can chuck it in the coin locker (usually max 3 days) or any baggage service centre and pay a small fee for it. Then you don't have to lug it around with you to Kawaguchiko.

Otherwise, say you're in Tokyo -> Kawaguchiko -> some other region : from Tokyo before you depart to Kawaguchiko, drop your luggage at baggage delivery. Get them to deliver your big luggage to the place you'll be going after Kawaguchiko. Pay a small fee, but free from all hassle. Totally worth it.

We spend 4 days in tokyo and 3 days in yugawara and the driving experience was the highlight of our stay. 3 days at Hakone area driving up to lake kawaguchiko and small tow of Atami. You can never beat the convenience of traveling by car. Imagine 8 of us including the children needing to waze through the traffic of people getting into the train.
Driving give you that convenience of traveling from point to point and you can cover a lot more in a day. Never mind the toll/ petrol and the parking charges. But i guess you have to be really confident to drive in a foreign land.
The tip is to ask your landlord ( mine was through airbnd) to rent the car on your behalf and you can get your car cheaply (I used 100 yen car rental). By the time you are at the car rental place you will be treated like a big boss. It was nothing like in other countries.
I was actually requesting to rent a car during my stay in Tokyo but my other landlord was against it. But when i dis travel around Tokyo, the traffic is not more congested as in KL and it is doable to drive there as well.
As for the luggage, i just put them inside the room during my travel.
Hope that helps.

I baby seat is one extra seat. You can't book an 8 seater mpv with 8 people with 2 baby seat inclusive. You need aomebody in Japan to help you with this. I has th same experience with ToCoo as well.
Other alternative is book for 8 people but rent the car seats there itself but there is a risk involve as well.

luggage kept in room of course no issue...the issue is when collecting the car from airport to accommodation...where to put the luggage ?