place the circuit in approximately final position but don't glue yet.
solder the input/output wires from the circuit to the proper input/output wires from the case, and the circuit outputs to the led's.
add batteries and make sure it works! after this it will be very hard to fix anything.
glue down and fully encapsulate the circuit with glue to protect it. hot-melt glue or silicone are good for this. be careful to keep glue out of the switch! also i positioned my switch pointing downward so that it does not collect water in the knob - even though it is a waterproof switch.
when encapsulating with glue, try to inject the glue into all the tiny crevices to get rid of as much air bubbles as you can, in case you take your bike to another altitude.