Data & Catalog in separate disk will improve the performance ?

  It will improve IO at the SO level, the catalog is in constant change, logs and data collector will require a high amount of IO(it makes sense ot separe them from the data store disks).

  Also look into storage tiers, it makes sense to map those if you have different types of storage for your "hot" objects. 

  Temp area should be set on a different disk.

 So yes is good to isolate yor catalog , temp area, storage tiers(based on access patterns).

  Disk size for the Catalog depends on your object number, logs size(cleaing), data collector configuration/retention, UDP`s , UDF`s.

  You might have a huge database with a small catalog.