Hey there,
I am Abraham, Senior VoIP engineer and consultant with robust and extensive PBX experiences and deep understanding and knowledge of SIP/WebRTC.
I've done hundreds of Asterisk based setups for various reasons ans situations and also already done many Yeastar TG100/200/400 configurations, S300 is also Asterisk based and I can get you done more than you need on that.
Please read more about me and contact me for details.
Regards.