Trouble/questions updating from 8.0.2 to latest


I'm working on updating an old 8.0.2 to the latestvVersion. So far, I found out I should first update to latest 8.0, then go and do every mayor release in it's latest Version meaning my roadmap looks like this:
8.0.2 -> 8.0.16 -> 8.1.12 -> 8.2.11 -> 9.0.11 -> 9.1.7 -> 10.0.4
So first I got stuck by the fact that 8.1.12 and 8.2.11 where no longer avaiable in the download area. They lead to error 404, file not found. 8.2.11 was fixed last week, but 8.1.12 ist still unavailable. Which is the first of my Problems
I did the upgrade to 8.0.16 which seemed sucessfull. Because the original version as that old and several times upgraded in a less then ideal way I used the "more advanced" Option in the manual and actually created a new folder. While everything seemed to work fine (no errors, database was available directly) I noticed that the calendar and contacts apps where simply gone. How do I reactivate them? The manual tells something like "click productivity", A button not available in 8.0.16 anywhere.
So my second Problem/question is: how to I reactivate calendar and contacts in older Version and, looking at my roadmap, is it necessary to activate those in every Major release? (I guess I should... I think it's updating the database)

Last but not least I read in the 10.0.3 changelog that it is possible now to upgrade directly from 8.2.11 to 10.0.3 which would save a lot of work. Anybody tried that before?

This is executed every night to make sure the upgrade path is valid.