Please refer to this document :
https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucme/requirements/guide/cme12spc.html1) u can connect a pc over VPN and use CIPC for example to make the employees make and get calls, but the VPN type should be taken into consideration meaninig that the CME should see the PC as part of the network (no natting in between) or it will cause issues such as no audio ... etc
2) from the link you can see that the max ephones for 2911 is 50 , but if you are refering to SIP Trunk sessions follow this link :
https://community.cisco.com/t5/ip-telephony-and-phones/how-many-calls-handle-by-cube-gateway/td-p/3059971