Maybe I shall buy the rigol ds1054z with its 12MB data but I have never used it.
24 MS with unlock codes. But whether you should buy it or not - it is up to you. DS1054Z has one very annoying issue - saving 12 MS buffer to external flash drive takes 15-20 minutes. I have not tried to connect it to PC, so I have no idea hoe that goes.
So can I use it as a 1kHz data logger for one 10seconds shoot at 1kSa/s ?
more is better, but I only need about this 20kB data (for 2 channels)
That depends if settings will allow you to go that slow.
Has this scope other data-logger limits ?
or can I record at any xx-samples per second for yy-seconds when the product xx * yy * n channels <= 10 MB ?
Can I zoom and unzoom on the screen, and shift before and after inside this delay ?
If you are talking about DS1054Z, then yes, once captured, you can look at any part of the buffer.
I read that siglent sds1104x has a better data-logger but I don't what can be better.
Maybe you might describe such examples...
I have no idea how any scopes perform as data loggers. Never used them in that capacity.