fly back diode for use with DC motors
but the store I bought it from still recommended and sold me a 10A07
  diode, the data sheet is in this link


The motor can be supplied up to 5 amps so all you need is a diode that can handle a peak of 5 amps (not continuous) and has a reverse working voltage that is at least 40 volts (a bit more than 30 volts).

A 10 A continuous diode capable of a reverse voltage of 1000 volts is of course perfectly usable but i question why a 1N400x wasn't recommended: -



It can stand-off 50 volts and handle a peak of 30 amps and probably cost a fraction of what you paid for the heavy duty diode (that can handle up to 600 amps of peak current).

Yes, I would still fit a reverse diode.