Yes, I work on Ancestry and just download to FTM as a backup.
I could work on FTM2017 and sync, but I find it easier just to work on one tree and use the other software to back it up.
I have re-named my old 2014 files and shifted their location to an external drive, so they will only open when I have the drive plugged in. There are a handful of notes and photos on those files which are not on my Ancestry trees (privacy precautions) and I will probably copy those to FTM2017 at some point.
I don't intend to make any further additions to 2014 and none of the databases for that version show on my 2017 now.