Hi Aditi,
Below are the few things to be noted.
#1. Identify the version/SP level in NW 7.3 & SAP JVM
#2. Run through UDA (Upgrade Dependency Analyzer) to get high level idea on the supported system
#3. Check for DB & OS support
#4. Check for browser support & compatibility
#5. Check for benefits that you are going to get specifically for your application (BPM/MDM-WD/WDJ)
#6. Plugin for WDC for 7.3 should be installed (I am pretty sure this will be taken care of by Basis/Admin team)
#7. All existing BPM processes in CE 7.2 should be completed. After the upgrade they will be lost.
#8. Also check if Portal Theme and screens are loading properly in case Federation is being used
#9. All the custom Java Application Parameters need to be reconfigured after the upgrade.
#10.You are using MDM-WD components, so please check for the SCA required and if there are any known issues.
There should not be much differences if you are using only these application which you mentioned. However, There must be a round of testing done in Dev/Quality environments after upgrading them. If all the applications run good in test environments, it will work in prod too. All the components of BPM/MDM/WDJava and WDC Components developed in 7.2 works on 7.3 as well.
-Pradeep