1. How much weight can this rack hold 2. Please advise part number for extra pairs of mounting rails.

The weight capacity of the product will depend on many factors including how the rack is loaded (weight evenly distributed), whether the rack will be on castors etc. We can confirm that the rack rails are made from 2mm CR4 steel.  

The part code for additional rack rails are R0883-M6-27. These are currently not available on the website, if required we would be more than happy to assist offline.