https://www.wirebarn.com/Wire-Selection-Guide-_ep_29.html for wire. Wire from wirebarn is solid copper, USA made, with GXL/TXL insulation (they discuss it a bit, an internet search will tell you more than you wish to know).
https://wirefyshop.com/ for connectors, get the assortment and their crimper. I use the wirefy terminals with the heat shrink collar. From their website:
"Crimp Heat Shrink Connectors Crafted from Premium Components
Pure Tinned Copper. We manufacture our crimp heat shrink connectors from pure copper for maximum current flow and minimal voltage drop. The tin coating protects your electrical connections against corrosion.
Brazed Terminal Barrels. Our brazed seam terminal barrels are superior to typical butted barrels because they do not split when you crimp them. Brazed seam terminal barrels ensure your crimp is rock solid, and the wire will not pull out of the splice.
Advanced Heat Shrink Tubing. Heat shrink tubing shrinks to 1/3 its original size, ensuring the tight and secure insulation for every connection. Heat activated adhesive creates impervious seals to salt water, oil, acids, dust and sunlight. These heat shrink terminals require a lower amount of heat, which reduces the risk of melting the wire insulation. We recommend using a crimping tool designed specifically for heat shrink connectors to avoid damaging heat shrink insulation when crimping. "
Their crimping tool is worth the money.