Super cool! I had a similar idea where I wanted to create such clones of some of my friends (with consent ofc) and see how well they know me. To extend your clone even more, you can also throw in every piece of digital text you have into this, eg. emails, notes, essays, blogs etc. I'm super down to work on LLM clones like these!

edit: I actually started a little work on this. If you wanna export more messages than the limited 40k, you can use [0]. I did and I have every text I've ever sent since I had WhatsApp.

[0]: https://github.com/YuvrajRaghuvanshiS/WhatsApp-Key-Database-...