A_A:
St Louis is a pretty good expedite area with a generally steady amount of freight, yearround. Like any area, busy depends on the company to which you might be leased, the area in which you live or are laying over, and the type of truck you are driving.
I recommend that you continue to read the forum, past and present, ask your questions here, then start talking to recruiters with the companies that advertise on EO. If you are in no great hurry, plan a visit to the "Expedite Experience" pavilion at the Mid-America Trucking Show in Louisville in March. Having done due dilligence to the business, you should then be able to choose a truck size and type, and a carrier that suits your personal preferences.