ownCloud interactions with databases and upgrading

In order to solve my owncloud 9.1.5 to 10.x upgrade problem, I would like to upgrade my php from 5.5.9 to php 7.0.15, Apache 2.4.7 to Apache 2.4.18, and MySQL 5.5.55 to MySQL 5.7.18. I'm currently running Ubuntu 14.04 and will eventually upgrade to Ubuntu 16.04, but before that, I'd like to put my PHP, Apache, and MySQL at the 16.04 versions (as above), run my present OC 9.1.5 now, and eventually upgrade OC from 9.1.5 to OC 10.0 or 10.1 (later). I like the idea of having 16.04's versions of the above working prior to migrating to 16.04.

My questions are:

How do I upgrade Apache, PHP, and MySQL in a way that doesn't break my current OC 9.1.5?
Are there settings in OC 9.1.5 configurations which need to be adjusted to the new Apache, PHP, and/or MySQL as above? I have looked at my owncloud/config/config.php file and didn't see anything regarding versions of the above (PHP, Apache, MySQL). Is the OC 9.1.5 agnostic regarding this or do I need to inform it as to my changes/upgrades?

Also, if anyone here knows, should I do the above, can I migrate back to my former Apache, MySQL,PHP versions should other things break or will that break my OC database? Of course, I will back up my OC database.

Also, I have a related question as to how OC handles metadata namely:
Suppose I'm backing up my OC database, say daily. Now suppose my OC server machine storage fails several hours after the database backup. Meanwhile new files have been added, deleted and changed post backup. Right before the next database backup, the harddrive holding the database alone, fails and my only option is to restore the OC database from the prior backup. The OC data itself is fine and I leave it alone. If I do that and restart OC with the old, backed-up database how will OC treat changes and new files which it obviously has no metadata stored for? Will they be added and/or updated again via the sync tools of the users, should they still exist on the user's ownCloud accounts? Will the now-orphaned files (i.e. files for which there are now no metadata) in the OC data cause any problems - other than taking up space?
so in summary we have this sequence of events:
1 OC metadata saved in database normal operation
2. OC database storage backed up at time t1, call it database_t1
3. OC continues normal operations with data changes - call them datadelta.
4. Database storage breaks at time t2. Just prior to breakage, database was database_t2 and OC server is now set to maintenance mode.
5. Database storage repaired and database_t1 restored. Database data are now back to database_t1.
6. But OC data metadata were in database_t2 while was lost.
How does OC react to this sequence of events? I imagine its data now could contain orphaned file which appeared between times t1 and t2 and were deleted by users prior to t2. What happens to the other data? Could I lose data under these circumstances?
Thanks so much,
5. Database storage repaired

Thanks so much,