Keep in mind that electrical problems are very often due to grounding issues. Proper grounding is very important. If your grounds are bad, anything in the system can act up, and it will be difficult to find out why.
Good wire is also very important. Marine tinned wire is the best. Here is one I use often:
https://www.amazon.com/gp/product/B0799HTZB5 The price is reasonable, and it is very corrosion resistant. For LED fixtures, I tend to use this wire:
https://www.amazon.com/gp/product/B01N0A16X2/ Very good tinned wire, easy to solder. There are many others, but try to buy tinned, marine wire. Do it once, do it right. Will save you many headaches.
DO NOT buy CCA wire! CCA stands for Copper Clad Aluminum.
CCA wire WILL FAIL in damp environments. AVOID LIKE PLAGUE! I can't over stress this.
As far as crimps versus soldering, you can use both, but I strongly recommend that you buy quality heat-shrink connectors with hot-glue inside and a quality crimping tool made for heat shrink connectors.
Make sure to use the right size for the wire you are working with. The wire should mostly fill up the crimp sleeve.
Strip, insert, crimp down and hold for a few seconds and then release. And then try to pull it off. Really. If you can pull it off, it's a bad connection, and you need to find out WHY. Was the wire gauge too small for the connector? Do you need to adjust your tension a notch? Did you put the connector in crooked or upside down? Remember, for pin-type crimpers, the pin needs to push into the solid side, not the split side. That is vital!
If the connection is solid, use a heat gun to shrink and glue the connector, and you will have a solid, reliable part. A little dab of dielectric grease before connecting helps prevent corrosion, especially in saltwater boats.
Once you get proper crimping down pat, you won't solder much. In fuse panels and behind dashboards, I almost never solder.
One notable exception is when I make up my main ground spider. (harness) For that, I run a 6 to 10 gauge TINNED main wire directly from the battery, depending on the boat. 6 gauge for a boat with a lot of stuff, 8 or 10 for a small boat with a few lights, depth finder and a bilge pump.
When making up the spider, starting from the battery, anywhere something needs a ground, I strip back some insulation, separate the strands and weave the jumper through the main wire and twist, then solder, liquid tape and heat shrink the outside Repeat as needed, and terminate at the ground bar or the negative side of the fuse or breaker panel. Good grounding is vital to prevent problems. All your major components should have their own direct ground wire to the main. This greatly reduces problems and electrical interference.
Another area where I always solder is when making connections in the bilge area for pumps, float switches and so on.
And a third area is @ the main battery terminals. Crimping is the primary connection. The solder fills the area and prevents water from wicking up into the main cables. MANY saltwater boats come in with cables that look good, but when you cut them 2" above the battery terminals, it's all green powder.
One note about soldering is to not go overboard. If you overheat the wires and the solder wicks too far, you can make that area very brittle. Use a decent soldering gun, rosin flux and a quality electronic solder and it's quick and relatively easy.
Once you learn the basics, you won't have many or any electrical problems.
