When soldering the wires on leds, better stagger the positive and negative poles, to leave big gap between + - wires, to avoid short-circuit.
The 12V neon sign led strip usually needs to be supplemented power every 2 meters, to avoid volt drop.
Our neon sign router bit is 4.2mm drilling depth, so your plexiglass better be 6mm thick or more.
Router Rotational Speed 8K RPM or more.
We have spray-paint led strip which is a bit waterproof IP55.
The best way is to use transparent silicone gel to glue on led strips to make it waterproof.