The answer depends on your goals as a student and musician. The market offers keyboards that have up to 88 keys. The ones featuring 66 keys are usually considered to be a safe choice for students who want to learn to play. If you go up a little and use a 72-key unit, then you’ll get to play a greater variety of music.
However, if you intend to use the keyboard to help you transition to a traditional piano later, it is recommended to start with an 88-key model. Still, in case you’re not sure about your sonic destination and goal yet, you might want to consider getting a 66-key model.
If you advance and need to upgrade to a keyboard featuring 88 keys, you can do that later. Also, many keyboard models have fewer than 66 keys. Such units are ideal for those of you interested in producing electronic organ music.