Hi,
This is with reference to your questions my suggestions are :
1. Go for SAP Finance holds 20% of share. Please refer to below pie chart it will make clear
2. You should go to institute for learning SAP Finance.
3. Yes, you should go for certification as nowadays many of clients asks for certified consultants rather than non certified.
After seeing the above pie chart you can easily make out that SAP is the best ERP.
Regards,
Tejas