Upload & Sell: On
I must have misunderstood, I thought you wanted answers to your question about formats and hardware?
If you are asking about what it takes to be a pro then I can tell you that one Pro I respect usually brings a Holga to his shoots. Everyone is different, everyone comes from somewhere, and everyone brings something unique to the table. You should decide what you bring. The bleeding edge of technology, does get pricey but the results are jaw dropping.
As to the question of cameras, format etc? Time marches on technology changes, and so do most Pros.
One aspect of the business that has not changed is that it takes a team, stylists, hair/makeup, assistants, models, location scouts, business people, reps, accountants, lawyers, hell you might even need insurance. Adds up to more than the cost of a camera.
One definition of Professional Photographer is someone who can fulfill the clients request on demand, as required. I guess that counts too.