I have the 9" DX and I use it regularly to read technical papers. It's just about the right size for that; I wouldn't want something smaller since there are already occasions when things get a little too small. I find it works reasonably well for reading and navigating PDF's (no detrimental delays).
Putting PDF's on a Kindle is easy -- just plug it in to your computer over USB and it acts like a flash drive.
I'm really not sure where to begin with my criticism of this article. Perhaps the McDonalds kitchen straw man. Or maybe the outright fabrications like:
"Big things, like obscuring the networking stack under so many countless layers of abstraction that it’s virtually impossible to even imagine what bytes are actually going over the wire."
The only actual examples of "incompatibilities" that weren't lies were trivialities -- who cares if DirectX is left handed or right handed? Flipping your Z axis is trivial.
As someone who has extensively used both .NET and other platforms (C++, Java, etc.), this article strikes me as the naive views of someone who hasn't learned enough .NET to form a cogent opinion.
Just so we're clear, lose money on every user, and try to acquire more users as fast as possible?
I work in the trading business, and in the trading business there's a running joke -- we'll lose money on every trade but make it up on volume! I didn't know people actually practiced such a strategy.
The 30" without question. You get 4 megapixels (2560x1600) on one screen instead of spread across two (2 x 1920x1080) - great for side by side columns of code (I can fit 3 on one of my screens). Its also very nice for gaming, although be prepared to experience some vertigo.
In general, machine learning would probably not be a great approach to day trading. There are several problems:
1) Limited market data: As an individual, you have limited access to market data. At best, you probably have real time top of book data but without paying for it, you almost certainly aren't getting a real time depth feed. Going off of only last trade data gives you even less to work with. In most cases free quotes are delayed making them worthless to day traders (although not longer term investors).
2) Limitations of market data: Even if you have a lot of historical data with a full order book, that is still of limited utility for simulations. The problem is that everything you do affects the market so any trade you simulate needs to be doing small enough quantity to not make your simulation unreasonable. How to deal with simulating market-affecting trades is a complex problem and the only way to truly know is to run your trades in the market.
3) For day trading, there is a lot of profit to be captured simply from the microstructure of the market (its moves back and forth, etc.). To capture much of this it helps to be fast but you won't be able to colo boxes at an exchange with only 10K.
Machine learning seems more suited to longer term investments and trading on a slower platform than making a quick profit arbing or scalping. You may want to consider this rather than day trading since not only does day trading require much larger amounts of capital, but its also extremely risky.
Also, if you plan to trade equities, enjoy all of the ridiculous SEC regulation (order marking, etc.).