Hi- My kitchen cabinet side panel (decorative piece on the cabinet, please see picture) came off. What is the best way to put it back? Thanks!

I'm installing a 1-1/2" oak butcher block countertop to support an aquarium, which will weigh at least 700 lbs when full. Will a 1x2 ledger bolted to the studs with lag screws be sufficient, or should I use at least a 2x4? Should I remove a strip of drywall and bolt the ledger directly to the studs, or will it be okay to bolt through the drywall? The countertop will be 25" deep by 54" wide. It will be hexagon shaped, so there will only be 14" of bearing on each side. I can also probably squeeze in a 2x4 support along the very back if necessary. This will be for a corner cabinet. I'll attach a pic of the cabinet as soon as it is assembled.