Dear Cindy
this will simplifies your problem. The challenge is now clearly lower to you. In this scenario the risks are lower. But may be you should use current/recent version which is EHSM 5.0. In any case: there are a lot of links in this FORUM related to this solution. Check:; SAP EHS Management for Beginners
You will find a lot of references to the EHSM solution; e.g. topic of data migration, set up etc.
In my opinion regarding dublicating of master data and the other risks you have mentioned. the riks is low.
Good luck in installation/preparation.
C.B.