Ledger and relations with customer & supplier accounts

Hi,

In case there are two primary ledgers within same business group:

1. Primary ledger X with Jan-Dec accounting calendar. 

2. Primary ledger Y with 4/4/5 accounting calendar. 

Both share same COA. Primary ledger X allows back dated transactions. Primary ledger Y restricts back dated transactions.

My question is:

1.  Can the OU of X ledger be shared with Y ledger?

2. Can all supplier/site and customer/site/account/ credit limit be shared between both the ledgers/OUs. 

3. Does it require to have a separate customer account / site for ledger Y. Will this affect bank collection on customer accounts?

4. Is it possible to make a single payment for a supplier/site for both ledgers/OU