My opinion is longer crack will give more control
The 114s will be fine for learning. You’re already used to them. Just get out there and begin riding, that’s the most important part. If you really want to get more cranks I would get the 125’s, or even 137’s but 145 is too long.
I think you’re right. Though pedal size (width) is a factor, I guess I’m thinking of my Freestyle days. That’s a 20" with 125s on a flat gym floor. Sharp turns to snap into spins and other moves; not stuff you’re going to be doing while learning.
145 is over-long for a 20". 114 and 125 are both good.