OK, sounds like you are not very specific in your questions because you are not very specific in your plans yet...
Let me begin to tell you about my own - very specific - transportation setup. I only transport firewood, but often over a distance of 300 miles. I use a trailer that is rated at 1500 kg/3300 lb, because my vehicle (2004 BMW 320d station wagon) has a tow capacity of 1600 kg/3500 lb. The trailer has high side walls, so I can really fill it to capacity. Towing the full trailer, I still get 30 miles per gallon of diesel on the highway.
My setup may not apply to your needs. But if you already own a vehicle with some towing capacity, buying a used trailer is a very low-cost way to start a transportation business. Of course, having a commercial truck, crane, fork lift, etc. gives you more possibilities, but at a much higher investment.