You have at least 3 issues:
First is the regulation aspect and as you seem to be located in Germany not many folks here (mostly UK-based) will know them.
Second point is already mentioned above, the busbars all need to cope with the maximum fault current & let-through (I2t). This is partly the heating effect, but also as you go above 100A then in the UK the rules start to require consideration of the electrodynamic forces that can bend conductors and physically damage them (and attached components). In a well constructed system, so internal faults are VERY unlikely, you might be able to rely on the downstream breakers to limit this but if not absolutely sure then you should consider the upstream fault current.
The third point is you have to avoid overloading the busbars. If your supply breaker is above the busbar capacity then you are relying on the sum of breakers fed off there to be lower than the maximum of the busbar. The could be exceptions if you can be use all are fixed loads so the breakers are only for fault disconnection, but in many cases you cannot be sure of that so with 10 poles on the busbar you ought to be no more than 12.5A average per pole (or whatever combination keeps the sum to 125A or less)
