100 hectares is 247 acres. Pretty big area.
1st, figure out the task e.g. no-till grain drill.
2nd how many hours are available to perform the task?
3rd, calculate hectares/hr required. If you want to plant 100 hecatres in 16 hours, you need to plant at a rate of 100/16= 6.25 hectares per hour (ha/hr).
4th, look up some available implements and how fast they can be used. 1 hectare = 10,000 sq. meters. An implement 1m wide traveling 1km/hr will cover 1000 sq. meters per hour or 0.1ha/hr.
If the implement is 6m wide and traveling at 10km/hr it will cover 0.1x6x10 = 6.0 ha/hr. Pretty close to the example target. It will complete the task in 100/6 = 16hr:40min.
Finally, contact the implement manufacturer and ask about recommended horsepower. You can repeat for various predicted tasks and figure out which one requires the most power.