TSD it said:

 Is there a field in the customer details which is unique per customer?

Yes, tCustomer.lID is a key field, but you need to use ODBC to access that field.  But so is the customer name, and it's not hidden from the user.

TSD it said:

Where can I find the definition of the TXT to import journal entries?

The program help for Importing Records doesn't explain it fully.  If you really want to 'roll your own' import, there is more documentation in the (free!!) SDK.  I've found that setting up the sample file and then exporting, then looking at the text output in Notepad / Notepad ++ is a good way to get the format needed for an import.

TSD it said:

Where can I export customer information with the set up credit limit and balance of outstanding amount (balance owing)

The credit limit is stored in tCustomr.dCRLimit, and can be viewed in the Customer List along with Balance Owing.  Balance of outstanding amount appears to be calculated 'on the fly' from customer detail, not stored in the tCustomr table.  It could probably be accessed programmatically as a query for the sum of all transactions for that customer in tCustr / tCustrDT, from the customer ID looked up in the tCustomr table. 

I would suggest searching this forum for 'Invoice Import' for more options, if the WinTree people haven't done an interface.

I hope that helps, please post back!

Randy Wester