There are many discussions on the forum about this subject, and the basic answer is that there's no issue with 2 or more versions of PD being installed on the same system.
In fact, the best way to be certain that the new version has access to all your existing content and downloads is to install it without first uninstalling the older version.
One potential issue is whether you purchase a new license for PD19 at full-price or if instead you pay a discounted price for an upgrade.
In the former case, everything will work like you've described with both versions available. If you pay for an upgrade though, PD19 will uninstall PD16 (although it should keep all of the existing settings).
Also remember that any projects created or saved in PD19 can never be opened in PD16, so it may help to make a new copy of your older projects for PD19 in case you ever need to edit the originals again in PD16.
This message was edited 2 times. Last update was at Oct 21. 2020 20:26