10awg - not difficult to make one with stranded wire and other parts from any home store
The power plant will benefit everything, regardless of the cables and allow you to ‘improve’ it over time as budget allows. At some point you’ll find that they are all really, really good just different - try before you buy if at all possible. $$$ does not always equal sound you’ll like
About 15-20% of the output wattage is wasted as heat - so if you’re system draws 400w, the power plant is ‘using’ about 80w.