As the others have said, the most important thing right now is a bike fitting.

Also you mentioned "drop down bars." Those are called aero bars and they would probably be a good idea for the kind of riding you're planning to do. But you should get those before the fitting so the fitter can set up the aero bars for you too. Then you'll want to start training with the aero bars now because they do take some getting used to.

The issues with the butt, wrists, back, neck, etc. should all get better with time in the saddle assuming you get fitted correctly on the bike. You may have the leg strength and cardiovascular fitness, but it takes some miles to develop the muscles and flexibility needed to sit comfortably on a bike all day.

I admire your determination and wish you the best of luck.