7.What is the maximum speed of the stepper motor ?

The ELS can send a signal at a maximum frequency of 100KHz. The maximum speed of the motor will then depend on the encoder resolution:

6400 steps/rev: 937 RPM

4000 steps/rev: 1500 RPM

2000 steps/rev: 3000 RPM

etc…

6.What encoder should I buy ?

You must buy à 5v compatible NPN open collector incremental encoder.

The recommended resolution is 600P/R but the unit can take care of all these resolution:

360,400,500,600,720,1000,1024,1200,1250,1800,2000,2500

If you are not sure, you can buy the package avaiilable on the website, the ELS and the encoder.