(This is really the only part of your question that isn't off topic as a shopping question or primarily opinion based.)

> Are there any advantages of the IS and better focus motor in photography besides the more stable handheld photography?

Yes, there are benefits to using IS when taking still images with a handheld camera. It allows one to use slower shutter speeds than would otherwise be the case before blur due to camera motion becomes noticeable in the resulting image.

Regardless of how good your handheld technique is, you can stretch that good technique even further using a lens with good IS if your subject is stationary.

On the other hand, if you are using your camera secured to a tripod for very long exposures or are using it to take photos of moving subjects in low light, IS doesn't do anything at all for you. IS has no effect whatsoever on subject motion.

For more about IS and its uses for still photography, please see:    

https://photo.stackexchange.com/q/49492/15871    

The same is true of STM: It is an advantage if you need faster, smoother, and quieter autofocus. It's not an advantage at all if you shoot astrophotography or landscapes and manually focus the lens.

For these reasons, we can't tell you if the extra cost is worth it *for you*. Only you can answer that.