Of all the cameras that I have owned, the X100S is my favorite.
The A7Sii only outputs at 8-bit. The Flame will record that 8-bit data and add two empty bits to create a 10-bit file but this will not improve the quality of your footage. The main benefit from recording with the Flame is that your footage will have 4:2:2 color sampling (much better for chroma keying and grading in general) and the compression codec will be much higher quality (Intra-frame vs inter-frame and a much higher bit rate)
Yes and no. While it's a very bright and "10-bit", it is not a wide gamut display.
Let me re state that- We are beginning to see a lot more true 10-bit displays released but many very high end and capable monitors still use 8-bit panels and FRC.
It's an 8-bit panel that utilizes FRC. While technically not true 10-bit, you won't be able to tell the difference and it will be more than satisfactory for it's intended purpose. There are very few true 10-bit panels out there. Most, including a lot of high end graphics and color grading monitors, utilize 8-bit panels and FRC.
The camera records those 120 frames into it's memory buffer and then converts them into two seconds of 60fps footage. (2 seconds x 60 frames = 120frames).