I prefer to go on what ive seen in the manga rather then speculating
Of course he didn't use it only 3-5 to,es
You are forgetting the 3 year time skip in which he unlocked and used it...
To even know he had it he had to have used it before...
When he talked to itachi he already hinted his eye was going bad.. So in that 3 years it messed him up a bit...
We have only seen one MS User from their transition of getting the MS to using a technique which is Sasuke and he seemed to just use it straight away without training
We dont know how many times he used it but Kakashi will probably go blind just not at Sasukes rate