As has been written several times in this forum, the templates are 5.0.1. capable. I myself have updated sites with template: kinvara, Koadline and LAYLA to J 5.
It's still important to have a working backup and know how to import it.
When updating to J5, a plugin is installed that is backwards compatible for some things. (Behavior - backwards compatibility) or something similar. This is switched on during the update and that's how it works for me. If I turn it off, it crashes. But I'm not an expert, I think the developer here has already described why and why somewhere.
Otherwise, your update will of course depend on the other extensions you have installed...
The system itself makes a statement when you try to update and the pre checker gives you the information!

Thanks for the info. I'll proceed with caution.