Mylo
Does it launch correctly if you try launching it again? If not, activate the venv (you can run the "activate_only.bat") and run `pip freeze`, check if TTS is listed there,...
That's not a critical error, it can be ignored
Try the common issues it gave the link for
from that first link you sent, it has the common issues, which includes a package you need to have installed, vc redist. (this is separate from the build tools) 
Try asking for support on the mecab-python3 github issues, they might have a better idea for what it could be.
There's a new notebook which will show the errors that occur during install. Although it probably isn't fixed yet. I'll see if i can find more information about the issue.
Is this only with xtts or also with other models?
I'll go through a few and see whatever errors i can fix then.
Alright, I'll fix this today
Although, fixing it would be another hacky fix for something coqui should do themselves. And I had plans to move TTS to an extension in #143. I should probably do...