You don't want to start a new system you're not going to keep. I keep customer files on my desk in portable file hangers. You can find them in nice plastics that look like granite. Office stuff is really sexy-looking now. Don't forget storage space for supplies.
Lighting is also important, and often forgotten until the last minute.
Telephone Services Businesses, even home businesses, need dedicated phone lines. Telephone needs are specific to each business. Every business needs at least one or two lines for the phone, a line for the fax and a line for the computer if it uses dial-up internet access. A hunt feature will route your calls from a busy line to a free one. Various private services offer voice mail, but phone company products tend to be the most reliable.