Support would answer questions like this however they would also help you develop a plan.
You are too hung up on this lines and keys thing, this is not a key telephone system, you don’t have a key for each line.
The line keys on the phones are extension appearances, you need as many line keys as you intend to have concurrent calls at that extension.
The ten phone numbers are irrelevant. These are digital trunks, the call comes in with a CLID (Calling Line ID) message that indicates the number the user dialed to reach you. You can use this CLID information to route calls.
The only relevant point for you is are you going to answer all of these numbers the same way or are the for different businesses? If they are for different businesses you can simply have the phone display the name of the business based on the CLID information so the operator knows how to answer the phone (done with inbound route CID prepend feature).
The side car for the receptionist is used to monitor extensions (the light comes on if the person is on the phone). You press the button to transfer the call from the operator to the user.
Experienced VoIP professionals know how to ask questions about your business and how you work so you can get the most out of a VoIP system without changing your business processes. Sure we can play 20 questions and you may be able to get your system working. Is that really a good use of your time or should you be leading and growing your business. While the software is free it is a large, feature rich system that requires experience and proficiency to implement.