How much RAM do you need?

I can recommend SuperMicro boards but it's just a guess because it's better to know what exactly do you want.

In case parent doesn't return:

fine with current hardware, based on >...done computer vision/machine learning with a much less powerful MBPRetina...

This describes the machine I am in the midst of building for my boy: https://news.ycombinator.com/item?id=11884519 I'm in the US and it the used Dell Precision T7500 [1] was about $300 including shipping. There's another ~$40 apiece in a new 120gb ssd and a new Nvidia GeForce 710 GPU from NewEgg. The 710 does ~350 gigaflops which is about $0.11 per, and better than anything else at a price that's rounding error on a high end GPU.

So why am I a fan of the Dell's? They're seriously robust machines. I've got a dual E5405 T7400 that's 8 years old. Last month on a whim I looked at the SMART stats for the original disk drives: more than five years powered on. Still whisper quiet. Never a hardware problem. These are machines Dell ships with a three years Next Business Day warranty. They're designed and built accordingly.

[1]: http://www.dell.com/downloads/global/products/precn/Dell_Pre...

I am afraid I am net an expert in AI and OpenCV, but I do know how to build a custom desktop. I would research what hardware other people are finding effective, and then just double check Ubuntu/Debian will have the driver support (its pretty good nowadays) for what you want. Building a rig is a great experience and quite fun too!