Your questions answered, to the best of my remembrance.
How did you know litho had failed?
This was over a period of five or so years! New stones formed over that period, so it wasn't a static environment.
As I remember it, I reported that there was little noticeable gravel passed in urine, and they did scans and found the stones were still largely present.
How many attempts did they try on each stone?
They didn't attack each stone individually, but as a group. I suppose at least three goes were had on each stone, on average. How many treatments you have will obviously depend on how hard are your own kidney stones.
How long did it take until they put you onto the Nephrolithotomy?
The nephrolithotomy was only for a single large stone that they thought was partially blocking, or could block, the flow of urine. This was a result of determining that further lithotripsy sessions would not 'roll that stone away'.
Also did you get any nasty side effects like vomiting (how long did it go on for)?
There were no side effects from the actual lithotripsy sessions apart from the minor pain of having one's back bashed for about half an hour! Analgesics largely removed that pain, which was simply a healing process.
After the nephrolithotomy, I was chucked out of hospital too early, and had to be readmitted for another night after I felt very unwell, and vomited when driving on the way back to the hospital (having first opened the car door, since you ask!).
In summary, I found the treatment for kidney stones was not really anything to worry about. Mine have gone dormant for much of the time since 2008, fortunately, and my status as "a kidney-stone former" seems to have alleviated.
I hope your treatment experience will be more successful!