Misc thoughts...
Legal
I don't know your background, but I recommend you get with the EFF and/or SANS and get a good idea of possible legal ramifications, e.g. if you choose to be an internet provider vs. an internet services provider vs. a private network provider or a telecommunications service or some mixture. These choices can really change the legal (and business) landscape for you.
Security
If you have a CISSP or equivalent, then you probably know what you are doing from a security standpoint. If not, then I recommend you proceed with caution--maybe take an intensive general course: physical security, protecting your customers, providing extra security services (IPS, DDOS protection, etc.).
Maintenance
Throw some money in the pot for monthly emergencies. Road work. Backhoes. Fibre splicing. Bad pink boxen. Converters. FX modules. Extra switches for fast swap-outs. A fast car and a fast technician who is fast with duct tape and bubble gum.
Network Diagnostics
You'll be doing a lot of proving "it isn't me." Get a fast laptop with an outstanding NIC and make sure you are up to speed with Wireshark and presentations. If you aren't a wizard with Wireshark, then take the 4-12 hours it takes to become one: memorize the hot keys, figure out the advanced filtering, etc. NMAP and SOCAT as well--you'll want to be able to show that your voodoo works, and perhaps even point the finger towards the real problems.
A Nice Suit
Don't underestimate the power of a nice suit. It reassures your customers. And that'll be 50% of your job. It's all about professionalism until they get to know you.
Your Audience
If your audience is 90% gamers, you might consider putting together a gamer's NOC. Web page showing pings and lag for various games... traffic flows, bandwidth, switch utilization, the most popular servers, info. Maybe host some games on local servers. Put together a small VMWare Cloud just for that.
If your audience is 90% online retail, maybe put in a Secure Zone, a DMZ they can host behind, maybe some Palo Alto firewalls that do WAP (web app protection) and SQL Protection and etc. Or just use an active IPS.
Etc.
Good luck!
--p