Its not hard at all , its something you can do in 30 - 45 minutes depending on your skills.. there are few tutorials online , here's one INSTRUCTIONS ...
I got my kit from this guy (Insaneamine from z-xtreme ) , really good quality and they look amazing...

 

They all do the same thing!

 

very simple for mine and most other kits i would imagine. i heard that the hks wires are a bit tricky because it is designed for the japanese engine bay which has the battery on the other side.

the hardest, and most fun part, was trying to hide all the wires.

 

First of all, you don't need such big wires to run some additional grounds...2 gauge - 8 gauge is probably WAY overkill. These wire are not grounding any actual components and are really just making up for any inefficiency in the OEM grounds. This means there won't be much signal traveling on that wire. You also don't need fancy connectors...the difference in resistance for copper/gold plated and standard is not even worth comparison and only good for the bling factor. Soldering AND crimping these connectors is also a bit much - most OEM grounds I've seen are just crimped and they seem to last years and years Get the right size wire for the right size connector and a crimp is all you need. Heat shrink is a good idea simply to protect any exposed part of the wire from corrosion and look neat/clean. I used 10 gauge amp powering wire on my car with standard 10 gauge connectors, crimped, heat shrink at the ends and used black wire loom to cover them all to look OEM and not stand out.