Special Periods are used for posting tax and audit adjustments to a closed fiscal year and there will be 12 Normal Posting Periods and 4 Special Periods. Transaction Code OB52, PPV is used to open and close the periods based on a/c types considering GL Accounts.

Vouchers containing line items and where Several Business Transaction can be identified particularly are known as document type. Document type controls the number ranges, Header part; IT controls the line item level.
Coming to Global Settings it is a 4 digit Alphanumeric, Name of the Company, City, Country, Currency, Language and Address.

Posting Key is a 2 character numerical key and it is special classification key and it determines Account type; Debit/Credit posting, Field status of transaction. Posting Key controls the entry of line items.

A charts account has to assign a chart of accounts to each company code. This chart of accounts is the Operating chart of accounts and is used for the daily postings in this company code. They have the following options when using multiple company codes. This can use the same chart of accounts for all company codes If the company codes all have the same requirements for the chart of accounts set up, assign all of the individual company codes to the same chart of accounts. This could be the case if all company codes are in the same country. In addition to the operating chart of accounts, you can use two additional charts of accounts if the individual company codes need different charts of accounts, it can assign unto two charts of accounts in addition to the operating chart of accounts. This could be the case if company codes lie in multiple countries. The use of different charts of accounts has no effect on the balance sheet and profit and loss statement. When creating the balance sheet or the profit and loss statement, choose whether to balance the company codes, which use different charts of accounts together or separately.

Chart of Accounts Key Contain the
a) Name
b) Maintenance Language
c) Length of the Gl Account Number
d) Controlling Integration
e) Group Chat of Accounts
f) Block Indicator.

Yes. One COA can be assigned to several companies.

The Account Group Controls the Number Ranges of GL account, the account group determines the fields that can configure on the G/L master record. It is necessary to have at least two B/S and P&L a/c.

It is not possible to use reconciliation account for direct posting since, When the data is posted into a subsidiary ledger, then the system would automatically posts the same data to the general ledger, each subsidiary ledger has more than one reconciliation accounts in the general ledger.