Your rain barrel stand looks good and sturdy. It should handle a 450 pound barrel of water easily. Before you set it in place, pour a small concrete pad to support it, and to avoid sinking into the ground and tipping. If you are going to use a 55 gallon barrel, you will soon find that the water doesn't last very long. I have four 275 gallon cubes that run dry if I am actively gardening. This is a double stacked set-up that I created. My other two cubes are single set-ups.
View attachment 152598
The down spout was redirected to the 6 to 2 inch reducer, which expands again to 6 inches. the lower 6 inch is where the first flush of dirty roof water goes. I have an empty Gaterade bottle inside that rises to the 2 inch neck to keep the dirty water from the cleaner water, which flows across and down into the cubes. the lower cube has a vent hose that connects to the overflow pipe just above the upper cube inlet. If we get a deluge that fills faster than the vent escapes, there is a 2 inch overflow routed into the original down spout drain. Not shown is the hose bib outlet glued in place later, and the clean-out for the 6 inch pipe on the other side of the stack.