I can only reach a 9th and I don't recall there being any parts that caused particular strain or injury.
Chopin had reasonably small hands, and I believe could only reach further because keys where slightly smaller in his day.
There is a section of octaves that requires a legato style touch, but this is usually done with a combination of 1/4 and 1/5 fingers to ensure the top note remains most legato.
You will find what your 5th finger can reach, your 4th finger can reach by slightly angling your hand outwards. The key to a lot of Chopin's playing is the angling of the hands.
Also, though mostly covered, bar 2 and subsequently most bars with any off beat rhythms such as that, I just make the first and last notes synchronized and everything in between is flexible.
I will listen to a couple of recordings to get an idea of the overall interpretation and work with that, but I certainly don't mathematically calculate everything, and then almost like a skill in it's own you can get better at improvising where to speed or slow down for different effects.
Sometimes for particularly long passages, you can use check points, so particular places where the notes should sync up and then again be flexible with everything in between.