can a router/hardware firewall suffice as a gateway?

hi;
im trying to set up a gateway to share internet connection and i need to focus on security.
i want to know if it is possible to get a hardware firewall which can be also used as a gateway? is it important to have a separate firewall and should the gateway be a server?

what are the advantages or disadvantages of these two methods?any recommendations on a good device for this purpose?

all help highly appreciated. cheers

haleem