Hi,
a) that's strange. Normally, the system should take this default. But, you can make a workaround by putting a rule of type Function module (FMDT_READ_MD_FUNDS_CTR) reading your fund centre and taking fund source from there. You should obviously put this rule before your NOT_RELEVA rule.
b) again, you can do it with Function module rule type FMDT_READ_MD_WBS_ELEMENT
c) again 
with Function module FMDT_READ_MD_ORDER. You can read data of statistical indicator into a USER_FIELD1 and then create another rule deriving FM assignment based on this field with 'overwrite' option.
Regards,
Eli