Difference between Michinoeki & service area

What is the difference between michi no eki and service area?

Also I found a website that has all the info for all michi no eki in Japan. Is there such website for service area too?

I don't know if there's an "official" difference, but a "Service Area" has a gas station and sometimes a small garage if you need repairs.

A "Miti-no-edi" sometimes has and sometimes doesn't have a gas station.

Both usually have shops and a restaurant with a lot of variation between them. The Miti-no-Eki also markets locally produced goods. One by Minamata is usually filled with mikan. One in Yatsushiro had a lot of igusa reed items. One I stopped at west of Shikotsu-ko in Hokkaido was filled with mushroom stores from end to end. I think it was called a "mushroom kingdom." Ones close to the coast usually have a lot of fresh fish. One in Aomori had lots of apples. The service areas along the kosokudoro usually don't have such a large a variety.

This explains what Michi-no-Eki are
https://www.michi-no-eki.jp/about/english

and this explains what a Service Area is.
http://en.driveplaza.com/rest_facilities/

As you can see, the big difference is that the former is located along ordinary roads which are typically accessible to pedestrians as well, and the latter is located along Expressways which are not typically accessible to pedestrians. They both don't have anything to do with the presence of gas stations, although the latter often has one.

I hope this has answered all your questions.

What is the difference between michi no eki and service area?
Just operating and management company and standing road side are different.
Michi no eki(s) are not on the Express way(toll roads of NEXCO mainly).
https://en.wikipedia.org/wiki/Roadside_station
SA/PA(P=Parking) are only on the Express way(toll roads of NEXCO mainly).
PA is simpler or smaller spot, no restaurant and gas station usual, but not all.
Several SA/PAs can enter anybody for free without having to be an express way user.

NEXCO = Nippon EXpressway COmpany Limited is 3 different companies, East, Central and West.
https://upload.wikimedia.org/wikipedia/commons/0/0a/Japan_Highway_Area...
Although this is a roughly their covered Japanese map,
but there are many roads of companies other than NEXCO on toll roads.
The main road as Express way connecting the whole country is one of NEXCO,
but the road in the big urban city and around managed another companies,
like Shuto-kou(kou means short of "kousoku douro" in JP) in Tokyo and around are so.
https://en.wikipedia.org/wiki/Urban_Expressways_(Japan)

East:
https://en.wikipedia.org/wiki/East_Nippon_Expressway_Company
http://www.e-nexco.co.jp/en/
http://en.driveplaza.com/rest_facilities/
Spots search is only in JP, but you can find other company's all roads.
http://www.driveplaza.com/dp/SAPAMap
(from map : 地図から検索 may find easiest)

Central:
https://en.wikipedia.org/wiki/Central_Nippon_Expressway_Company
http://global.c-nexco.co.jp/en/
http://globalsapa.c-nexco.co.jp/en/sapa/facilities/
https://globalsapa.c-nexco.co.jp/en/search/currentlocation/
SA/PA spot search is only in own area.

West:
https://en.wikipedia.org/wiki/West_Nippon_Expressway_Company
https://global.w-nexco.co.jp/en/
https://global.w-nexco.co.jp/en/restareas/sapa.html
SA/PA spot search is only in own area, but EN map with.
http://www.w-holdings.co.jp/ (in JP)
http://www.w-holdings.co.jp/en/map.html

Umi-Hotaru is neither NEXCO nor Shuto-kou, but is one of the few examples with a large SA.
https://en.wikipedia.org/wiki/Tokyo_Bay_Aqua-Line
https://www.umihotaru.com/en/
Also some SA and PAs exist in btw Sanyo and Shikoku area.
http://www.jb-honshi.co.jp/english/guide/use.html

If you like cars and no busy in weekend night,
Daikoku PA in Yokohama is the best for watching custom cars nearest Tokyo.
https://youtu.be/uUt6wlwr1Zw