RE: Extending the PSU cables.
I'm surprised no one has suggested a terminal block. they keep the original spade terminal, are quick to connect, and cheap.
Here is one option i found: https://www.mcmaster.com/5566T85/
print yourself a cover and call it a day
RE: Extending the PSU cables.
On this topic. When going to the more flexible wire, I would go one gauge larger diameter for current capabilities. Wire gauges are based on diameter, not current capabilities. As there are more strands, you have a larger amount of air gaps that don't carry currents.
Over my decades of experience, I have found that crimp connectors are not the best when vibration, movement and heat are involved. They do fail and I have replaced hundreds in the field. Proper solder techniques with a heat sink to prevent the solder from flowing into the wire when soldering the connector is the best idea. In rough usage areas, I have done a dual crimp and solder where I crimped part of the connector and soldered that in place and then crimped the rest of the still stranded wire.
Also, adding a bit of support at the connector, like the flexible nylon that is used for the cables on the print head will help minimize the flexing.
Of course, it all depends on the usage the connectors will see.