Putting the business aspect aside, start by building a couple of wheels from scratch. It is not as easy as you think. You must ride the wheels you have built, otherwise there is no point. I would start by building city bike wheels first, as the building aspects of these are less extreme than for high tech MTB.
For a basic, city bike front wheel consider the following consumer prices from Bike24 (im based in europe):
-1x 622-19 Rim Mavic A119: 20 Euro
-36x 2mm straight gauge spokes, sapim/DT swiss: 12 Euro
-36x 2mm brass nipples sapim/DT swiss, 4 Euro
-1x Shimano Deore 9mm QR hub, 15 Euro
-1x Schwalbe HP Rim tape, 2 Euro
Sum: 53 Euro
Besides the parts you will need various tools that help you build the wheel. Truing stand, dishing tool, spoke wrench, and possibly a tensionmeter. I have professional grade tools for about 600 euro, but you can get away with alot less. Wheel building is a fairly involved and expensive undertaking. But if you want to learn more, start with the guide made by Mike T (attached).