Well, the modem isn't going to be the problem there. Any cable modem will work, all it does is link the coax ISP network with the local network. For a business, I would say it would be best to rent the modem from Comcast just because you'll be able to be sure it works. Just rent the modem, not the router.
If you really want, I have this modem:
http://www.amazon.com/Zoom-DOCSIS-Cable-Modem-5341J/dp/B0063K4NN6/ref=sr_1_1?ie=UTF8&qid=1422636468&sr=8-1&keywords=zoom+cable+modem It works quite well at 130Mb.
The router is what will give you the VPN access, and all the other security features you'll need. I used this one:
http://www.amazon.com/Cisco-Systems-Gigabit-Router-RV320K9NA/dp/B00DGH08OC/ref=sr_1_1?ie=UTF8&qid=1422635373&sr=8-1&keywords=cisco+rv320
Most Cisco routers are troublesome and quite slow, and that is because they're vastly underpowered. This one is better than the rest because they actually put a decent processor in it. (I've tested them all. It was quite expensive and quite annoying.) The RV320 was the only VPN router that didn't preset problems for me. It is pricey, but it is worth it.
However, it doesn't provide wireless. You'll have to get a separate wireless access point. This is actually a good thing because Cisco is HORRIBLE with wireless. If you want to secure you wireless with something that won't be hacked in half an hour, go with a small business AP from Xclaim or Genius. Again, they're expensive, but that is the only way to get secure wireless.
In my quest for more secure routing and wireless, I have found another alternative: pfSense. It does have VPN capabilities, but I have not tried to use them yet. This is an OS/software router solution. The software is free, you just need to install it on a low power system. It's actually more secure and more stable than any hardware router I have found. It doesn't even need to be a new system. Old hardware works quite well, as long as the hardware is reliable. I put it on a VM on a ESXi 5.5 Hypervisor using only 256MB of memory and 1 virtual processor core, utilizing the rest of the host for a FreeNAS storage server and a backup server. (All that on one box.) It takes time to learn to build that kind of system, though. You can search Google for instructions on setting up the VPN in pfSense. There are several sites for that. I just haven't put the time in to try them out.
Those are a couple choices. You can choose from them.