One of the most common questions I am asked is the difference between Touch Sensitive and Weighted keys, and which is ok for piano playing.
Ideally if you are wanting to play the instrument like a piano, or indeed having piano lessons, you will need weighted keys. This means that the instrument will feel like a traditional piano, and you will be able to get all the levels of feeling and expression from your music. You will also build up the proper finger muscles.
The Yamaha Clavinova, both CLP and CVP range, all have weighted keys, and are ideal for piano playing at all levels.
If you can only go for a less expensive option, the a Touch Sensitive keyboard will do. This means that the harder you play the keys, the louder the sound will be, this allows you to get some expression from your music.
As a rough guide most new Yamaha keyboards above £170 will be Touch Sensitive.
This type of instrument will do for a short time for piano lessons but to take piano playing further you will have to invest in a weighted key product.
The other consideration is the number of keys the instrument has. Most keyboards have 61 keys, this is 5 octaves. On a piano there are 88 keys, 7 and a quarter octaves. All Yamaha Clavinova have 88 keys. If you start with a 5 octave keyboard you will very soon run out of keys in your piano studies.
Of course 5 octaves is enough keys if you are playing as a keyboard. i.e. with a split point for your left hand to play the chords, while using the automatic accompaniment.
Feel free to call me if you need further explanation.