Hi, Anjali,
This note will help you. Regarding other things--
Timeline - Depends upon the business scenarios.
Advantages - DP can do forecasting with better option compared to ECC (much more flexible), SNP does the network planning (ecc can't do that) and PPDS can do prodction planning and capacity planning with many heuristics provided. Other information you can find in help.sap.com
Regards,
Anil