Since I didn't find any TTS + VC setup guides that were worth the time it took to read them, I decided to make my own setup.
This is a guide for anyone who needs a Text-To-Speech + Voice Changer setup that just werks.
download and install MorphVOX Pro
download and install VB-CABLE Virtual Audio Device driver
install Audio device changer for Firefox
open windows control panel and change "Sound" settings like in pic 1
set "Tools > Audio Devices > CABLE Input" in firefox
open MorphVOX Pro and change "Device Settings" like in pic 2
select a voice of your choice then enable "Morph" and "Listen"
open vrchat and change settings in "System > Microphone" like pic 3
This is all you need. To start using TTS open Google Translate webstie in Firefox, select the language you want to use, then type the sentence you want to say ingame and click the speaker icon to read it like in pic 4.
If you want to test the setup beforehand, you can use Audacity, change the device settings like pic 5. Start recording and then press the Listen button in firefox to read your sentence.
After recording, click stop in Audacity and select "File > Export Audio" to save and listen to the result. It should sound something like this: https://my.mixtape.moe/cdfzrk.wav
You can use this setup to play music ingame too. In Foobar, go to "File > Preferences > Playback > Output" then in Device section select "CABLE Input" and click ok.
Note that MorphVOX will affect Foobar playback too, before playing any music turn off the "Morph" option in MorphVOX.
Ask a trusted player ingame to help you test things out to make sure your volume isn't too loud nor too low (high volume spam can get you banned).