1.No. You cannot apply stop loss on the same day i.e the day you "Sold" a stock. You will have to wait to get the credit of the sales proceeding in your demat account.
2.You need to have equivalent cash or more For your purchase in your ledger and not just the margin money to cover your trade loss i.e. Stop Loss.
3.You cannot use this cash for the next 3 days i.e T+2 settlement period. You will presume your cash will only be available at the end of T+2 days for the stocks you sold from your demat account.
Allah Knows Best...