Opening First Period in GL New SOB and Receivables Manager

1. We are importing Open Receivables Transactions from Old SOB to New SOB in Receivables for 5 Orgs.

3. Which  should be the First Opening Period in the General Ledger and Receivables? 4. We are closing our old SOB on 30 June 2011. We only want to import Open Transactions in new SOB. Suppose there is an Open Receivables Transaction which has a Transaction Date : Feb 5 2007, GL Date is 30 June 2011. 
For the same Open Receivables Invoice. The client want to keep the original transaction date i.e. Feb 5 2007 in New Receivables Manager Responsibility. But want to Post them to 30 June 2011 of new SOBs.
The other requirement is that Users should not accidentally post anything before 30 June 2011.