I took delivery of my first uni this week, a Nimbus II 20" wheel. I’ve not tried it out yet, as I am waiting for delivery of my wrist guards.
It came with 114mm cranks.
As a complete beginner, are these shorter cranks likely to make learning harder?
Shouldn’t make a huge difference. 125s are a common size. 114 is only a tad shorter. I ride 114s on a 28.
For a beginner you probably won’t notice, it’s all hard 
But I did find riding a 24 muni with longer cranks than my 24 did give me more control and better backwards ability. (still no good though) I have a feeling 125s would make things a little easier = save one or two hours in the basic learning stage… the average is about 15 hours I believe.
Cheers
When I bought my first decent 20, it had 125s, and when I bought my first 24 it had 150s. The ratios were the same: The crank length was half the wheel radius.
A 20 on 125s is fairly easy to ride, but then a bit limiting.
114s are only 11 mm shorter than 125s. That’s a reduction of less than 9%. It’s about the same difference as riding a derailleur geared bike 1 gear higher or lower - a matter of choice, rather than crucial.