Joe,
Thinking big is always a good idea. That ensures that even if you don't hit your big target, you'll at least be closer to big than if you were aiming small. Start off w/ local business, and I think that will keep you busy for a while. You'll be surprised at the fortune you can make by just doing business in your region.
The most important thing you need is a positive first impression. The first question in your prospects mind should not be "Can I trust him?". Rather, it should be "What forms of payment does he accept?".
I really think that E-Helpdesk can instill this positive first impression in your customers. It gives people the impression that you are a big company.
We recently setup an E-Helpdesk account for two brothers in the IT consulting field. You can check out their demo account here:
http://demo.e-helpdesk.net/ntconnections
What we did for them was
1) Offer them a professional looking website. This is one of their most important marketing tools. Customers are directed to their website to read more about them. This is what I mean about the positive "First Impression". People want to see that you at least have a web presence.
2) Offer their client's a way to contact them to request support. Notice the Login box at the right. This is the same type of online ticketing system used by big corporations, except it can be run for a fraction of the cost. This type of functionality allows the "mom & pop" shop to look more like a Fortune 500 company.
3) Offer them an efficient way to run their company by using technology. If you are starting out as a one-man operation, you'll need a way to complete as many jobs with as few resources. As the saying goes "Time is money". You can't rely on pen & paper if you want to achieve your goal of going Nationwide.
My biggest barrier when I tried to start an IT services company was being able to compete locally w/ so many other established businesses. Just open up your Yellow Pages and look under Computer Services. That is why I built E-Helpdesk to give me a competitive advantage. I decided to use E-Helpdesk to assist professionals like you, rather than use it for myself.
If you want to chat more, feel free to PM me your phone number and a good time to call. I'd like to give you a free account to help you get started if you are interested.