1. After the revolution, how to you prevent the people that were influential during the revolution from seizing power for themselves, becoming the new bourgeoisie. This happened time and time again in practice.

This hasn’t happened “time and time again in practice.” What do you mean by a “new bourgeoisie?” How familiar are you with Marxism? You may want to read the book Blackshirts and Reds for clarifying and contextualizing the myriad successes and failures of AES states historically.

2. Even in the best case scenario, the decisions on what to produce become centralized in the hands of politicians. Political systems that we tried so far don’t work that well in practice. Is this really the best solution?

Again, please elaborate. Centralization is a natural consequence of market-based systems over time, therefore Marxists see central planning of public property to be the next phase in Mode of Production. Marxism isn’t about trying to force a new society, but moving along the natural progression in Mode of Production.

AES states have not been perfect, but they have dramatically improved on previous systems. I think a good intro to the process of historical development would be reading the short essay Why do Marxists fail to bring about the “Worker’s Paradise?” You seem to believe Socialism to be something that can be implemented by decree, by fiat, rather than something that forms over time. The laws of a system depend on the Mode of Production, the capacity for democratization increases alongside centralization and increases in the productive forces. This process is why Marx says the bourgeoisie produces “more than anything, its own gravediggers.”

I’d recommend reading the second link before the first, the second article gets to the heart of your issues and takes around 20 minutes, the first link is a full book and is generally a good read, not as immediately relevant.