(a) for any aircraft Type, the answers to the TC questions will be in the Type Certificate Data Sheets, AFM, and Weight and Balance Manual (the latter may have various names, though).
(b) for the following - Datum Constant, Moment Constant - the values are quite arbitrary as it depends on the design philosophy of whomever runs up the loading system.
The general form of the index equation is
IU = C1 + ((FS-TD) * WT)/C2
where
IU = index unit for trimsheet data entry
C1 = a constant (optionally) used to get rid of negative IU values
FS = the fuselage station location of a particular load per the OEM aircraft datum
TD = the datum chosen for the loading system (referred to the OEM aircraft datum)
WT = weight
C2 = the non-dimensionalising moment to IU constant
Note that there may be metric to imperial (or vice versa) conversion factors hidden in the equation's constants along the way.
(c) for Operating Empty Index - there are various definitions around so it is important to check that you know what is in, and what is not in, the definition of the day. Otherwise, the form will follow from the general equation.
(d) freighter version - balance arm of the pax compartment usually would not be the way to go as the errors would be too great. The actual loading system structure for any given loading system is particular to the system