I have a domain that already has a number of wordpress installations in existing subdirectories.
I would like to activate wordpress multisite to manage so new subdirectory installations with a new template.
The concern I have is that on activating multisite it's prompting me to clear all database tables for the existing installation. Will this cause a problem for the 20+ existing installations?
Typically, each instance of Wordpress has it's own database. If you have 20+ seperate Wordpress installs, then you should have 20+ different databases. Each database is going to have quite a few tables.
If it is asking you to clear the database tables, then it is most likely only referring to the data for a single Wordpress install: namely, the one your are installing Multisite on. In other words, your 20+ other Wordpress installations should be safe.
However, when installing Multisite, it is always a good idea to back up your databases.
As far as using it to manage your sites, I'm not sure if multisite is the best solution. There are plenty of plugins that will perform the function you need, without having to manipulate databases.
