Nothing is pre-determined per se

I don't think too hard about how everything that happens is inevitable, but that is the logical conclusion

These seem to be saying the exact opposite of each other - if everything is inevitable, it is therefore pre-determined.

As for the relation between the physical (chemical, biological, etc) processes of the brain and consciousness, you're absolutely right that the latter necessarily arises from the former, but that does not mean that our consciousness is reducible to just those processes. Consciousness is an emergent phenomenon and, even if we were able to trace all the physical processes of the brain, we would still not be able to entirely explain our subjective experience.

For scientific socialism, I think relying too much on a deterministic outlook creates a very sterile, complacent ideology. Look at the pre-WWII communist parties of Europe, who were positivistic determinists par excellence. They believed wholeheartedly in the inevitability of a socialist revolution, and look where that got them. I think a more productive view would be to embrace the inherent unpredictability of human action, our capacity to break out of a given historical moment. Nothing is guaranteed or pre-determined (however probable), and it is precisely because of that fact that our actions are meaningful, that praxis is a worthwhile endeavor.

I hope this doesn't come off as too critical, I appreciate you sharing your views comrade