If you are nervous about your first dual deploy, you can actually "simulate" a dual deploy launch at no risk beyond single deploy. Simply load your airframe for single deploy (main in sustainer) and fly it with your electronics plus motor as a backup charge. Set the motor delay to be a little after apogee. If all goes well, the dual deploy electronics will pop the main at apogee with the motor eject just in case things go wrong plus the nose should separate at programmed altitude. You can even stuff a small parachute in the payload to make sure your harnessing is correct. However, do not skip ground testing....
Wires disconnecting is a legitimate concern. Using the wrong type of wire, not securing the wire, over/under torquing screw terminals, etc can be a problem. You can pull on the wires and bend them around a bit to test out and look for weaknesses. Having proper strain relief really mitigates wires breaking at attachment points. You might just want to ask someone to look things over prior to your launch. Most people are happy to do it and you'll get no shortage of opinions.
Soldering the Eggfinders have gotten a whole lot easier now that Chris is supplying them with the GPS module already soldered on. Definitely practice, but there really are only a few components now. I always have to look up which way the silly LED goes on.