How do I open up my Mac to remote sharing anywhere?
I would recommend the screens app and screens connect. The software is not only fast and works excellently, but it helps diagnose if your network conditions are not correct to accept incoming traffic past any firewalls or NAT borders. 


https://edovia.com/en/


For ssh, I use prompt and recommend that as well. 


https://www.panic.com/prompt/


Together they solve all issues like not knowing your IP address of your router or having to set up dynamic DNS.