Parking/camping/driving a campervan: problems

Hi everybody,

I'd like to rent a miniature campervan from July 10th till August 21th (I'll spend the last 8 days in Tokyo and I won't need a campervan there). I�fm also specially interested in a full coverage insurance. Any idea/suggestion about that?
And here are some questions:

1. Insurance. I'd like a full coverage insurance with self-risk reduced to 0 JPY and including:
- Super Collision Damage Waiver - SCDW
- Gravel Protection (I don't know if there are gravel roads in Japan, maybe close to campsites etc.)
- Tyres, undercarriage, windshield
- Theft Protection
- Road assistance

2. Highways and tolls
Some rental companies offer an ETC device. I will try to avoid Expressways because I'm going to drive short distances and then stop to visit places. Is it possible to drive ONLY in normal roads without paying expensive tolls? In Italy or Spain it is, and it's... nicer :)

3. Overnight
a) Is it possible to park in a normal city spot to stay overnight? In many blogs they say that, if the vehicle is small, you can. But I don't know what does "small" means to Japan.
b) Are Michino-Eki areas only along the Expressways?

4. Campsites
I see there are a few nice campsites, above all in the countryside. But in their pictures I only see tents! What about campers? I don't refer to RV, but to the medium-size camper van. May I have access to a campsite with my camper van?

Thanks in advanced for your advises and all the best!