How Delta works for 0CO_OM_CCA_9 extractor and other points

Hello Experts,

I would like to know how delta works for 0CO_OM_CCA_9 extractor? As per Table ROOSOURCE , its shows Delta as 'ADD' means Additive delta which what i understand is if Old record has key figure as 1000 and changed value is 1500 then delta will bring +500 in the PSA.

if my understanding is correct then how we can design the data flow in BW?

Question 1: If requirement is to have a custom DSO and then to cube, do we have to make all the key figures as 'Summation' in the DSO? Please suggest the Design flow in BW with DSO as a requirement.

Question 2: I checked in table COEP, there are millions of records , we are bringing CCA_9 for the first time? what should be the ideal approach to load in BW for the first time and then how should be initialize Delta?

Question 3: COEP has many 88 fields, and Extractor has far less fields, if requirement is to have all the 88 fields in the extractor then how we can enhance standard Extractor 0CO_OM_CCA_9 for extra fields from COEP?

Kindly share your thoughts.