USB 2.0 capacitor inrush
But how much capacitance can i have without creating to big current spikes during charging of the capacitors?


You can have as much capacitance as you want. You just have to limit how fast you ramp up the voltage on those capacitors.

You can google "inrush current limit circuit" to find circuits that solve this problem. Or, if you're using a switching supply, you can look for one with a  "slow start" circuit.

If you have some part that has a maximum voltage ramp-up time (some digital circuits are like this) powered by the same supply as the big capacitors, that might limit how slowly you can ramp the voltage, and thus limit how big your capacitors can be without violating the current limits for USB.