Hi Rahul,
It us good to know that you are interested in doing SAP. As I said there is no hard and fast rule, try to gather the information as much as you can from the website's with regards to the module and the training institute and then proceed further.
As far as I am aware there are jobs for freshers for an entry-level with a less package, but once you gain the experience with thorough knowledge, then you will have a bright future. SAP is an ocean and day by day there are new things that gets added. So you should learn and practice as much as you can, by understanding the basics.
With regards to the course, my personal advice is not to quit your current job. Try to manage with your current job and join the course and struggle for a month or two. After which take a leave for 10-15 days and prepare for your certification and give a shot.
Once you are done with your certification, start looking for job's through the institute which you discussed with and once you have the offer letter then leave the job.
Leaving the job at the moment to join the course, which I don't suggest.
Wish you good luck.
Cheers
Venkat