You will need a permit for this job so start there before asking us to evaluate the design. Codes vary so much the building department gets first say. They will also tell you the correct size of the footing, post sits on top of the footing not inside the tube. Most large lumber yards and box store will carry that 6x10 hanger. Simpson Strong Tie HUC610 6x10 Heavy Duty Joist Hanger Concealed/Reverse Flange