You should spend some time watching RR Buildings on the 'Tube. Those brackets are not "sheet metal"...they are heavy, welded steel and designed for the specific load and column size you will be using for your post frame structure. And the bolts you use are also substantial products designed for the job. (simple Tapcons are used for initial positioning but very heavy, specially designed fasteners are driven down into the concrete after drilling and evacuating the concrete dust. The significant benefit of using them on poured piers or a stem wall is that zero wood goes in the ground. I suggest you not use sawn 6x6s; rather use laminated posts. Why? They will be straight, true and stronger than sawn posts, especially at those lengths.