If you don't make IP calls, then SRV values don't really matter... for more look here
If you don't know what NAT is, it most likely should be enabled (and keep-alive as well). In such case you may not need SIP ports (I assume 5060 or 5061) forwarded to ATA
Having STUN server doesn't hurt, and if VOIPo has its own - you should use it. There are also numerous public STUN servers

None of these values are specific to your adapter. There is plenty of info for all of them on the web.