The best kind of people to start new businesses or work out their ideas are generalists, not specialists. This is because the day-to-day rigors of running a business will demand you wear multiple hats everyday. This is not the time to box yourself into a stereotype and claim “that is not really my area of expertise”. I am all in favour of focus on your strengths and outsource your weakness, but you more often than not, you would still find a need to get an intermediate skill level in such areas.
To become the best businessman you need to be might include not only the things you enjoy doing like buying goods in bulk, but also the things you do not like doing like online marketing and basic accounting. You have to embrace such and get a good feel of it before you eventually hire a specialist that will then fully concentrate on that aspect.
The early founding team of any company or NGO alike must be diverse and the people involved must be able to deal with some amount of ambiguity over their exact roles as they will often need to go with the flow.
Specialists are needed at big companies where everything is planned out already. Generalists are needed at small, nimble and fast-moving startups, that is just the way things are.