Making a recent purchase of SX10s was probably a bad idea to start with as the end of life announcement date on them was 30 July 2019, with the End-of-Sale date being 3 days ago (28 January 2020), so they're already an out-of-date device. Although, that's possibly why you were able to pick up a lot of them cheaply.
If you have that many of them in an organisation, having them all as standalone is not recommended - and generally won't work very will without some form of call control platform to handle all your NAT requirements on a single broadband link (and not having a fixed Public IP address certainly won't make the job easy either).
If you have a read of the "SX20 as standalone" discussion you will find information on setting a single device up as standalone. You can use this to test one of the devices, then try to replicate it elsewhere - but you'd be much better off using a proper call control platform (on-prem with a CUCM or a VCS, or consider registering them to the Webex Cloud).
Wayne
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