That's gonna be tedious
Is the words order important? Will I have to try all the combinations?
Yes words order are important. No you don't have to try all the combinations but only pick a word, goodluck to that.
I think your saved phrase is in order already because you copied it obviously. Now like the other poster said here, maybe you accidentally erase the last word (I will assume it's the last word). What you will do is to try all the words and put that as a last word. Again, goodluck to that.
Since your OS have been reinstalled there is no trace already of the Electrum stored in your computer which maybe can help you to skipped those word phrase but it will be a technical and we need knowledgeable person here to guide you.