It’s all easily replacable; I’d recommend just removing the bulkhead locking nuts and pulling each segment out as a subassembly, vs. cutting anything! (This lets you duplicate, or at least reference old plumbing when redesigning/rebuilding!)
— Not all bulkheads are created equal; I’d recommend steering clear of ABS plastic bulkheads when selecting replacements for the display tank, specifically!
— it can be worth ordering your gate valve (and possibly unions) online; they are a relatively pricy item(s), and I’ve had mixed results with typical big box store examples! (Things like the knob being extremely sticky and difficult to turn “right out of the box”…)
It would be worth looking into making this tank have dual drains; a “herbie” style drain configuration… then, just plumbing the return up over the back of the tank! — the current plumbing configuration through your two bulkhead holes is a single drain, and single return! (This configuration is notoriously difficult to keep quiet!)