Train from Miyazaki station to Hakata station

Hi....need some help for train service from Miyazaki to Hakata:

1) Is it necessary to book the train tickets in advance? If yes, when will the booking open if I travel in Nov 2025.

2) The whole trip is make up of 2 different train company?

Is it necessary to book the train tickets in advance?

No, the trains also carry unreserved seats, which can be used without prior booking.

If yes, when will the booking open if I travel in Nov 2025.

Seat reservations can be made from one month before travel date.

2) The whole trip is make up of 2 different train company?

If you take limited trains all the way, then the entire journey will be by JR Kyushu. If you take the shinkansen between Kokura and Hakata, then you will be taking two different companies (JR Kyushu and JR West), but because both belong to the JR Group, you can get a single ticket for the entire journey.

Note that there is also a bus/train option via Shin-Yatsushiro, which is generally faster and cheaper (but the B&S Miyazaki bus should be booked in advance). It is explained here:
https://www.japan-guide.com/e/e8001.html?aFROM=2161_8000

Or you can go via Kagoshima. And it will be the one company. JR Kyushu.

Of course! I still forget sometimes that with the "recent" extension of the shinkansen to Kagoshima, it is now faster to travel via Kagoshima than Kokura. Over an hour!

Thanks to all for the useful information…

B&S Miyazaki ticket includes both expressway bus (Miyazaki - Shin Yatsushiro) and Kyushu Shinkansen (Shin Yatsushiro - Hakata). Obviously, domestic flight between Miyazaki and Fukuoka is the fastest. JL and NH fly this segment.