There are so many options because outer world may vary so much.
They needs to be set according exact configuration of Asterisk server, according the network topology, according supplemental services you will provide, according upstream connection you have, according country you are living in and many others.
I'm claiming we can advise you nothing ?
Configure basic Ext1 parameters so phone will connect to Asterisk. Configure codecs used/prefered (you should avoid transcoding whenever possible thus follow Asterisks preferences). Leave rest default.
If you will hit a issue, collect symptoms and describe them here. We will try to identify the cause and settings that should be tweaked to solve them.