If I am importing a custom object using the CSV data import wizard, how do I create a "Date Created" field and also change the "Last Modified" field on the object.
It doesn't seem like such fields exist.
[SalesForce] Data Import Wizard for Custom Object (Mapping Date Created / Last Modified Fields)
Related Solutions
There should by no fundamental difference between custom Master/Detail and Lookup fields - except that Master/Detail is always required.
In the Screenshot below you find a custom Object TestChild__c to be imported with a custom lookup field TestParent__c. As you see, you can match Lookups either with their Salesforce Id or with their Name.
Apex data loader is the best. You can do all the functions using data loader. I guess you are using Enterprise edition with NPSP so data loader will work for you.
Best Answer
Created date is created authomaticly after insert of record. But you can also import value for this field - you have to create case to salesforce support. Only they can give you permission to set this field value.
Please check: https://success.salesforce.com/ideaView?id=087300000006to7