Hi Basis Team.
1) Can we install Content server our existing ECC system box.
Yes, It possible, but try to install separate system along with Maxdb, because it stores the documents,pictures, & video's files, trimly it may required more disk space based on your usage.
2) Where can we download the content server software
3) Installation procedure
You can refer the SCN link. SAP Content Server 6.50
Regards
SS