I noticed an interesting thing: almost everyone who starts learning Spanish at first does not worry about numbers at all. Usually people think that numbers are the easiest topic. But then a moment comes when after uno, dos and tres, long words like veinticinco or setecientos appear, and the brain starts resisting a little.
And usually the problem is not even in the numbers themselves. Spanish numbers simply look unusual for an English-speaking person. Especially if you try to learn everything in one evening.
In practice, everything is much easier. When you start regularly hearing numbers in speech, seeing prices, time, or dates in Spanish, numbers gradually stop feeling like “a mess”.