Hi wakaka,
If you choose correct mosfet and correct excitation voltage, mosfet going to
linear (ohmic) region, when turned on.
In this case power dissipation will be RDS * I².
I is maximum motor current.
RDS-on can be determind from transistor datasheet.
If power dissipation in each transistor are greater than 600-800mW it needed heatsink.
Regards,
Davood.
Added after 38 minutes:
sorry i dident saw current rating before.
I think you must use good power MOSFET like IRFP150 or better with use of a good heatsink.