Hi,
a. After the sucess of init if souce have chnaged or newly created records then only delta will pull records other wise nope. thats i suggested to do some changes at source with help of sd team.
b. at info pack you just select delta update mode. at LBWE(source system) you need to schedule V3 job for your data source.Click on job control, set time and date,period values to run your V3 job.
V3 job will pull records from source to RSA7. Later you can delta info pack at bw side.
Thanks