Bitcoins are not sent FROM addresses.  This is a fundamental misunderstanding of how bitcoin works. Continuing down this path while trying to understand Bitcoin at a technical level is only going to cause you more confusion.


Do not re-use addresses.  If you want to re-use an address, then either make sure that you use software that will allow you to simultaneously spend ALL unspent outputs that were created from that address in a single transaction, OR accept that you will be giving up a bit of privacy because you chose to re-use an address.

Addresses are NOT account numbers.  Bitcoin is not a bank account.  Think of an address like an invoice number.  It's something that you give to someone else so that you can keep track of the payment that they make to you.  You wouldn't typically re-use an invoice number, so don't re-use an address.