Hi Nisha,
1. First of all, How would I determine which info structure is being used at this time in my company?
I need to know this so that when I am creating my own custom (S500 - S999) info structure, i can copy the existing KFs and Characteristics and add them to my info structure and then Add a specific key figure on top of that.
Info structures are nothing but tables so in se16 you can check which are Info structures are having update values.
Yes you can add the specific key figure on existing self defined info structure in MC22 after that you need to generate it.
2. Can multiple info structure be in 'use' at the same time in any scenario?
For self defined info structure are application specific you can not have multiple info structure for same scenario. If you take the example of flexible planning with self defined info structure then you can transfer the demand from only one info structure.
Regards,
R.Brahmankar