Should I use all these template files or will theme hooks do the job?
The module that defines a template defines if it is a template or a theme functions, that's not something you have any influence over.

And yes, theme functions are faster, but they're also deprecated and will be removed completely in Drupal 9 (Because twig is far easier to write than PHP). With render caching and so on, the performance difference is no longer as relevant as it used to be.

The performance difference is between having a template or not. There's anyway a template, just not a custom one, and the only performance difference then is the additioal complexity that your template adds and what you are doing sounds trivial.

There might be reason to do what you're doing differently, you could use preprocess, but you'd need to at least share your templates/code (you should always do this when asking questiosn) so you can get a specific code example. But not because of performance, a more valid reason would be code/template management, it will be more work to make further changes if you have 10 different templates or just one.