So, I haven't tried this software, but it's called Medibang Paint and supposedly it's meant for drawing manga, it's free and cross platform.
There's also Manga Studio 5. It has tools for making comic frames and doing speech bubbles. As mentioned above, you probably don't want to limit yourself to templates, but MS5 does offer a library of page templates if you need it -- I never use the template stuff. It's easy enough to make your own layout.