Hi Aditya
The green/grey status relates to the Check vs Do not Check
The proposal column of Yes mean it will be added to PFCG when important. The ones that count for impacts is the YES values (although some might need to be switched to NO and others on NO switched to YES).
In relation to answering your questions about whether needed or not - that is the challenge. Below is a very good blog by Otto Gold regarding SU24. If SAP consistently managed the SU24s then you can trust the values (mostly) and you'd have your list
SU24 related OSS notes with SAP Support
Figuring out what proposals are necessary come back to reviewing the transaction (with some functional knowledge and general experience). The activity is not a repetitive tick and click but an analysis of the proposals to determine if they are valid.
For cleanup of SU24, I wrote a comment about Full Proposals, Partial Proposal and Empty Proposal in this thread. How you set this will depend on the transaction/authorisations and your roles.
Prompt for Authorization Object
To limit how much you have to work through - go to AGR_TCODES and extract all your customer roles. This will get you all of the transaction codes in scope for your solution. Hopefully, the number is not too high. You could then break them down to reports/display vs master data vs system transactions and attack them that way. Eventually, you will have to maintain and regenerate the impacted roles (which SU25 will help with).
Regards
Colleen