I bought the new Dell XPS15 with 32GB RAM, 1TB SSD, and Nvidia GPU the week it was released, and straightaway installed Ubuntu 18.04. It is powerful enough to last me three years and the price was good.
I am mostly happy with it - superfast, great screen. The two problems I had were when installing the Nvidia drivers, plus the fans stay on more than I think they should.
Rather than waste hours trying to solve these, I have decided to wait patiently and see what the community and Nvidia come up with.
Would I recommend others to buy one? Yes, though perhaps wait a while if any of your key requirements are not yet fully supported.
You can get a combined dongle like the Dell DA300 that combines Ethernet with VGA, HMDI, and DP (if you are doing customer presentations you need all three unfortunately.) That is what I use rather than carrying around a couple different dongles.
I love the Dell XPS 15 9570 with 32GB and a 1TB SSD. I have a docking station (TB16, although the D6000 looks okay too) and I run two 4K 32" monitors with a wireless keyboard from it as my work desktop.
It is thin, light, long battery and I feel like I am not making any performance sacrifices.
I would try Fedora 28, or if you are a bit more technical- Arch. I'm running Arch on a 13" and it works flawlessly. I've had a lot better experiences using Fedora when compared to Ubuntu.
If you want to use Arch but are not that hardcore-technical (command line installer etc.), try Antergos. It's like Arch ez-mode -- GUI installer, installs with a GUI of your choice (Gnome by default), uses all the Arch packages. I am running Antergos on a Lenovo Ideapad 720s and it's a pleasant experience.
Regarding the loud fan you should be able to run with NvidiaPrimus or Bumblebee - I provision laptops like this for my developers and switching off the Nvidia graphics to only use it when it's specifically requested really saves on battery. Also there is the TLP configuration which can extend your battery to a decent amount of time.
I am mostly happy with it - superfast, great screen. The two problems I had were when installing the Nvidia drivers, plus the fans stay on more than I think they should.
Rather than waste hours trying to solve these, I have decided to wait patiently and see what the community and Nvidia come up with.
Would I recommend others to buy one? Yes, though perhaps wait a while if any of your key requirements are not yet fully supported.