Having done another 15 miles today, the creaking noise is coming from the handlebar, as opposed to the suspension fork. Also, sometimes the pedals are making a clicking noise, I suspect when the gear change is not completely right. So far, no creaking noise in the seat post or saddle.
As the bike has done more than 100 miles now, I think it's due for its first service/check anyway. I believe the second one is at 500km, and then 1000km. Interestingly, the service booklet from Kalkhoff indicates that those are not free of charge, as they are "normal service intervals".
Are people getting those checks for free from the UK shops? I believe my two issues are going to be dealt with under warranty anyway (which, incidentally, would be a lot longer than the 2 years advertised, given the SOGA in England, and the price of the bike).
I have now emptied completely the battery after its first charge. The battery symbol on the LCD display showed an empty battery, but the assistance seemed to continue going for a while, although at a much lower level. I was expecting a sudden cut-off, as opposed to reduced assistance for a while.
Finally, the LCD display just switched off completely.