I wouldn't be married to the idea of using the Focusrite clock. There might not be any advantage at all due to how clocking works. As to the preamps themselves, they are adequate but nothing that makes you sit up and take notice. They will get the job done especially as auxiliary 8 pack. What are you recording? Non-classica/non-acoustic?

I bought the octopre mkII 6months ago, it's an honest sound for an honest price. I meen, it sounds good but not great.. somehow transparent without coloring
I sold it 3months later and got a UA 7-10 specially for it's features and versatility. (but it's not in the same price range)

So if you need more inputs ; go for it.
If you need better quality or a different sound, or with more mojo or a warmer sound compared to your motu, better continu your research

Thank you for your input.
I am looking for a transparent sound, I can do all the coloring (or not) after recording.
I will be recording mostly rock combos (drums, electric guitars ...) nothing classical.

It will work just fine for your needs. Again, not something to write home about but also not something that has enough of an individual audio signature to detract from the source.