No. Kits are gone. It was too much of a hassle to make kits. Or at least, that's what he said last time I asked RCF.

As far as "dupont" connectors. Your usually looking at the super ancient 0.1 inch / 2.54 mm spaced connectors. You can buy pre-made cables, or make your own with a kit like this:

https://www.amazon.com/gp/aw/d/B06XSH87M8

You will also need a crimper. I like this one:

https://hobbyking.com/en_us/handy-crimp-tool-complete-set.html

But your free to buy any crimper you want. Or even try to get away with some pliers, technically.

On your other question regarding beds. You can try any method you want. Most VORON CoreXY builds use a beefy relay that pulls directly from your power socket. This reduces the wattage on your control board. But also means you need to be careful since your dealing with mains voltage. (Over 50 volts)

Different strokes for different folks. You can try double sided fiberglass pcbs, or silicon heat pads. You can use aluminum, steel, or whatever framing you want. You could use copper or glass for a even surface. You could use PEI for a adhesive surface. Depending on how high Temps your after.

Hope that gives you some ideas.