So I work in a company where we have a linux machine acting as a router/firewall, and I like all the control you get in this kind of setup compared to having a consumer grade router that ISPs usually give you.
Knowing that, I decided to build a Mini PC to have the same kind of setup in my home, kind of as described in this guide: http://arstechnica.com/gadgets/2016/04/the-ars-guide-to-building-a-linux-router-from-scratch/
So the computer in question would act as a a router, DHCP server and firewall, but I have another linux server already in my home, which runs a Teamspeak service that is accessible from the internet and a few other services that are only for my LAN (a Samba server, for example), and I've read somewhere that it is not advisable to run services that should only be accessible to the LAN on a firewall machine, for security reasons. But it would be way more convenient to have only one machine running both my router services and LAN services such as the Samba server.
The question is: Is there any way I could make this setup work and make this new machine which is going to be the router/firewall run my LAN services in a secure way, making it impossible for the services to be accessible from the web?