Bitcoin mixer - You Might get caught by authority and need experience to operate
Bitcoin exchange - Need to start small and have to spend thousands of dollar on ads and rewards during start without any guarantee of profit in future
Bitcoin wallet - Hard to make any money but will have great responsibility of fund security and other legal obligations
I think its better you first start something small hiring a team from freelancing platform on contract basis, if you get some success proceed to make it big or if you fail learn from it and move to next venture.