Hi,
Since the future of Acymailing is at v7 I definitly rocommend to go with v7.
As you've found out you can have both versions on your server. That's because these are two entirely different versions each having their own set of database tables. That way you can continue with v5 and get familiar with v7.
Basicly you install v7, migrate your data and start testing. Make sure your license (in case you have Essential or Enterprise) remains attached to your v5. Do your testing and when satidfied migrate your data again, so your data matches yours in v5. Then swiotch the license to v7 and continue from there.
The migration is described here: https://docs.acymailing.com/setup/migration. Please not that if you have Smart Newsletters you manually need to recreate these in v7 as Automated Campaigns. When you move production to v7 you also need to recreate your subscription forms, otherwise new users will be subscribed to your v5 instead of youyr v7.
Here's the v7 documentation: https://docs.acymailing.com/