Since Jay already helped you with templating a title (and you marked his advice as a solution), you got only one question left about “font size for title”. Suggest to discuss it in that huge card-mod thread if advices provided here are not enough.
A general remark.
You got Entities card with N entities.
And you need to make a title dynamic.
For this you decide to place the whole Entities card into the config-template-card (CTC).
Then you will probably have to add all entities used inside the Entities card into “entities” option of CTC - otherwise the inner card (here - Entities) will not be updated inside CTC if any of these entities changes.
Means - the whole inner card will be redrawn, not only a corr. row.
If you decide to add a graph card inside CTC - this redraw may cause flickering.
So - you should use CTC only when it is really needed - or entities inside inner card rarely change.
Using CTC only to template a title is not a good idea.
Suggest to use a markdown instead.
Here is an example.