Looks like a good experimental thing if anything so please behave yourself accordingly for that matter and it really doesn't look good at all. I can't see what usefull could be done with such small plate when you can buy something like old PC for like 10 EUR and it will be better.
I thought about using an RPi for my screener, actually. I use them for all sorts of stuff. I got one set up as an MP3 stereo, one set up as a chart plotter for marine navigation, one as a very portable computer with an ethernet port. They are a lot of fun to mess with. The problem for trading is the graphics. Graphics are verrrrrry basic and you want high resolution and lots of real estate for trading with for instance Trader Workstation, IB's platform. You don't need blistering speed or umpty troglobytes of RAM and a processor that runs at Warp 9. It is nice to be able to support multiple large monitors, though. Keep in mind that your choice of desktop trading platforms will be severely limited, too. Raspbian, the usual operating system for these little boards, is a stripped down Linux. You can probably run Ubuntu, or Debian, but you will want to use a very simple desktop. A RPi doesn't IMHO have enough muscle to run a VM very well so no WinDOHs. You could maybe try ReactOS which is still in Alpha but I don't have much confidence that you can run a Windows desktop trading platform on it at this stage of development. If you want a cheap trader machine, get used, or a refurb, or a return. Or a clearance item. Open box. If you have one that is just old and slow and in the way, you could install Ubuntu on it, and run TWS and presumably ToS but no other platforms will run natively on Linux and I wouldn't trust Wine or VM with something like that that could cost you money.
TOS runs very well in Linux ( I have it on Debian Stable, Ubuntu and Mint). The only caveat: you must install Oracle Java. Otherwise drives 4- and 8- port NVS video cards without a hitch
Not to derail, but have you also used TWS on Ubuntu? How do you rate TOS against TWS, on Ubuntu? I am running TWS and it seems to work nicely but I haven't used TOS. I am trading on a Dell refurb with Ubuntu 18.04
A $25 Raspberry Pi Was Used To Hack NASA’s Mission System https://truththeory.com/2019/06/23/nasas-mission-system-hacked-by-exploiting-raspberry-pi-device/
https://betanews.com/2019/06/24/raspberry-pi-4/ a 64-bit processor, dual-band 802.11ac Wi-Fi, and Power over Ethernet (PoE) via a HAT.
THIS you could trade with. Two 4k monitors, not too shabby. More is better but two is a pretty good foot in the door IYAM. Practical, if you already have the screens and other peripherals laying around. I would get the official power supply. I would want a full size keyboard and a touchpad and give the official peripherals a miss, I think, for trading. Ubuntu MATE would be a lot more flexible and usable than Raspbian I think, and I would be irresistably compelled to test it with full blown Ubuntu. You could install apps straight from the regular Ubuntu repositories and I bet ToS and TWS would install from there prospective websites and run pretty good. I think I would want to add a HD or SSD. If nothing else, to keep a rolling backup in case the SD card packs it in. I really like the 4GB RAM. Nice. Would also make a nice dedicated screener machine. The main argument against using the RPi 3B is the lackluster graphics performance. This new version goes a long way to improving that.
I had a look at the newly released RPi 4. Yeah it has 4k video. Yeah it supports two HDMI monitors. But it does not claim to fully support two 4k HDMI monitors at the same time. So not quite what I was thinking, but maybe still doable. I ordered a board and power supply (requires a bit more power than the 3B, and used USB-C) but it will be some time before I see it. Initial stocks went pretty quickly and nobody seems to have them in stock. Also if you like using a case, the 3B case will not fit the new model because the ports have changed, so you would want the new case made for it, or 3D print one. You would probably NOT want any of the keyboards commonly used with RPi. Get a USB keyboard, full size, and a good quality touchpad or mouse, also USB. Wireless gear can fail or batteries run down or get interfered, and you could be stuck in a position while it is going bananas on you. I mention that because it is very common to use a slim wireless keyboard with onboard touchpad or joystick with these little computers. Not a good idea for trading. Anyway I will have mine probably late next month, and I will give it a try. Otherwise I will attach a hard drive and use it for a media player. The 3B I am using, with the outboard amp and speakers, plays music okay but is not really good for watching movies, no matter what monitor is plugged into it.