equipment 2

Do we need to adapt the diameter/length of the fittings? We are planning to use a circulation pump.

You have to think of the hinoki tub as a large basinet. It is simply set on the floor and not connected with any piping (a part for the case of a pump). The faucet is wall mounted and the water flows into the tub. Often the drain is not even connected with any fitting: the water flows out from the bottom towards a floor-drain.
For the pump fittings: you can let us know the exact location of the outlet and inlet so we can prepare the openings.
Actually, opening the drain hole (of the right size, in the right location) on site is the probably best option as the tub is made of solid wood and opening the hole is very easy.
We do not have availability of fittings with diameter/threading matching the connections of your pump. You should request the pump manufacturer fittings at least 3" long. (the tub wall is 42mm thick). In the worst case, you should be able to have fittings custom made in your country.