It can be a bit of a hassle yet ANY off the shelf bike is less hassle than a custom bike which is what I have. Yes the Clari and Sora shifter are difficult for small hands so it always perturbs me that these shifters are fitted to youth bikes. Just another example of the disregard that the bike industry has for youths/small people. The Shimano Tiagra, 105 and Ultegra levers should be pretty much the same however. A few years ago when I bough levers they were the same. Its a matter of fitting wedges or adjusting the lever travel. Also individual cabling on each bike becomes an issue. If the cabling is fitted poorly which adds friction then this becomes an issue. Also the size and curvature of the bars has a great impact on how the levers perform for small hands as well.
I'd be very surprised if you could get Ultegra cranks in anything shorter than 165mm. When it comes to short cranks just be thankful that you can get ANYTHING. I had to have my short cranks engineered.