I like Jogeswara Rao Kavala's as well as Rakesh Mane's suggestions about setting TECO.
To achieve the 2nd part of your requirement - to set status CLSD - you may schedule the batch program SAPLKO99 (t-code CO99) using the parameter RESZEIT to specify how many days after TECO you'd like the Orders to be automatically business completed (in my experience, you might want to allow up to 90-270 days for external Order invoices to be posted...)
