Hi Neha,
SAP HR/HCM is definitely a great career option, but you have to keep in mind that it is changing very fast.
It also depends on what you are looking to do in the SAP HCM Domain; there are a whole lot of options available. For example, you could be a Functional Consultant, Technical consultant (ABAP), Admin, and others.
You also have to realize that SAP HCM has changed a lot. Now, with SuccessFactors, they are offering cloud solutions for all Talent management processes like Performance management, Goals management, Compensation, Recruiting, Succession management, etc.
Since SAP has already made it very clear that Cloud is the way forward, I believe that focusing on SuccessFactors may be a better deal (here I am not saying SAP on-premise is not moving forward).
Also, many of the SAP HCM Consultants have already jumped on this bandwagon and are working on various SuccessFactors projects.
My advice would be that if you are looking to permanently work on SAP HCM/SuccessFactors only some online training would not help.
Certification will definitely help you in the long run. Also, nowadays, clients are looking for Certified Professionals. You can get a lot of information on the SAP/SuccessFactors sites (Certification details, course materials, costs, etc.).
Also, do remember that the CORE HR Process knowledge is very much essential in the SAP HCM Consulting business as you would not be able to contribute or perform for the client if you are not able to understand the various business processes of the client.
Lastly, getting into the SAP HCM/SuccessFactors field requires a lot of hard work, commitment, ability to learn, and update new technologies. So, once you are into it, then there's no looking back.
Let me know if you have any more questions.