Are you seeking help to make this happen - or - are you asking about the possibility of it being hacked?
I suspect the latter, so ...
Most NAT routers will, by default, provide excellent protection against remote access - the translation process allows outbound connection requests, noting these in a table in memory; any inbound traffic corresponding to a previous outbound connection will be routed to the requesting host, but any inbound connection request, without a corresponding outbound connection will be discarded - the router, with no entry in the NAT table to match it against, has no idea which host it is meant for, so in the bit bucket it goes.
I want you to note, the preceding paragraph never mentions the firewall - it's all done by the NAT (network address translation) process running on the router. If you never forward a port in your router, and your router does not support upnp (or has upnp disabled), preventing ports from being fowarded by hosts on the network without your knowledge, there is just no way to get past a NAT router - even if it has no firewall.
How safe is your particular setup? That would depend on how your router/firewall is configured.