What speed package do these people have with Verizon FiOS?
I'm not sure what you know about networks, so forgive me if I am telling you something you already know. But depending on the connection speed (15/5, 50/25, 75/35, 150/65, 300/65), and what this business does for a living (law office or a medical practice) you don't want the Default Gateway of your network also being your Firewall (aka the connection to the Internet).
I would suggest, since you are already planning on upgrade the 1GB switch from a 8 port to at least a 24 port I would look at the Cisco SG500-28 or SG500-28P (if they need POE). It is a Layer 3 Switch, so all Broadcast traffic (aka junk traffic) including but not limited to connection to their local server (or NAS) etc. run on their local Cisco Layer 3 switch. Then I would either get a small Cisco ASA (once again not knowing their speed) or even a Sonicwall (I have a TZ200 here at home on my 75/35) and add a route to the route table that says something along the lines of "ip route 0.0.0.0/0.0.0.0 192.168.1.1 (192.168.1.1 being the LAN interface of your firewall unit)
I don't think it would be wise to purchase a Cisco 2800 or even a Cisco ASA5510 for your WAN traffic because A.) both have a limit of 10/100 and B.) 12-16 people wouldn't generate enough traffic to even hit 5% of port utilization. Even though some people may disagree, a Sonicwall in a commercial environment, I think would be ideal for the 12 - 16 people. I have their NSA3500 on a 20/20 fiber and approx 60 people and we barely break 10% port utilization.
Also, another bit of information (aka food for thought) is don't think what you need today, think what you're GOING to need 3 to 5 years. Most of your purchased (not leased) computer equipment qualify for a depreciation, so if you have the money now I would look at that $870 SG500-28P (POE Layer 3 Cisco SMB Switch) if you can afford it because you MAY go to a VoIP service through like 8x8 (a hosted VoIP Service), etc. etc.
But until you're able to answered the bases, it's hard to tell you for sure.