A wise man once said
'12 volt won't kill you!' 'but god dam it will burn!' (and that can kill)
Pro Tip #1 - Fuse Everything!
There is no excuse, no fuse equals fire hazard, 12v Dc does not electricute but it certainly does burn good. All positive circuits must be fused, the fuse is there to protect the cable not the item, rate the fuse to the cable, and rate the cable to the job.
Pro Tip #2 - Solder! Solder! Solder!
There is no better connection, naturally water and corrosion resistant, solder provides the next best connection.
Use crimps terminals only where necessary and use a professional crimper, not the dodgy $2 ones or you will get a dodygy $2 connection.
Lastly, definitely NO scotch locks or twist and taping, that's just a quick recipe for disaster.
More tips to come, please come back soon.