Hi,
To start with, version 6 is stable so you can safely use it. If you should migrate or wait depends on the v5 functions you want to use, since not everything is added to v6 yet. Acyba is doing a tremendeous job to bring back all functions to v6.
Both versions use their own set of database tables, so you can have both versions on the same site. This way you can continue to use v5 and get familiar with v6. You can migrate your data at any time.
Version 5 is still supported and maintained by Acyba and I am sure they will notify you in time when they plan to stop development or support for v5. For now it's way early to make concerns about this.