Aquarius

The Mattel Aquarius is something I almost given up on, since most of the the systems offered on EBay are way over my budget. In fact I did not even expect to get this when I placed my €40,- bid for what I thought was only the console itself. To my surprise and great joy I did not only win the bidding, but found myself with a really complete spread. Including the tape recorder, a printer, all the original books and even four original games.
Normally I refer to the articles on The Register, but this time I also recommend reading this section of the RetroArchive since it's got the best story of the Aquarius. As both articles really make clear the Aquarius was one of the biggest flops in the 8-bit computer era.
Multiple sources on the internet report that the standard Basic is supplied even without a FOR NEXT loop, but that's not true.
There's not as much information available on the internet as for the Spectrum or Commodore C64, and it's much more scattered but I found the following sources very useful:
The Aquarius section on the website of M. vd Steenhoven.

Mattel Aquarius Thermal Printer

One of the many peripherals designed for use with the new Mattel Aquarius home computer system is its thermal printer. This is strictly a one-system printer; it connects directly to the Aquarius console without additional interfaces, as do the other Aquarius peripherals.

Mattel Aquarius Printer

The Aquarius printer offers 40, 5 x 7 characters per line (10 cpi) at the rate of 80 cps. It is capable of printing 256 characters including upper- and lowercase letters, numerals, and special graphics characters. The printer will accept special thermal paper 4-3/8 inches wide.
Although the printer looks really fancy and if it was specially designed for the Aquarius, it is in fact a Alphacom 42 VP thermal printer, which was also used for the Commodore C64 or VIC20.

Composite Video

As with all my retro computers, having a composite video output is one one of the first requirements. Geordy Rostat at notANAN has a description of his attempt to do this. Amplifying the existing video signal so it is suitable for a standard monitor is what I've done so far on all my Sinclair computer,so this seemed like a good solution. Ed Snider on 'The Zippster Zone' however mentions the possibility for a different solution, using the raw RGB signals. This seems like a nice option too, when combined with my GBS-8200 video converter board.
Third option would be the composite video modification found on the  Intellivision wiki.

And recently I found this : https://aquarius.1stage.com/aquarius . There are complete instructions on building a video amplifier circuit, and even a link to a ready made PCB.