Yes, yes and yes. I'm from one of those who don't have luck? hehe But i manage to solve almost all the problems.
Anyway, just look at the forums, many other people have problems with upgrading, and for some of them i don't have solutions/haven't seen those errors so i suggest read forums very carefully so you have "picture" in your head just in case something happens and you will have knowledge how to fix it / or at least you will find it fast. If there's no solution here, contact Plesk Support.
How many clients do you have on server? If you many clients don't even try to do the upgrade on working days and daily, only in night and weekends. If you stuck with problems, then everything will be probably down 1-2, maybe 3 days and if you can accept this downtime and you won't have any problem with clients (which is not acceptable in 99% cases), go for it.