Hi hi! Glad you like the game-- and I will def be making more like it in the future, don't worry about that! ;D
As for the voices-- okay! So, there's a system in Ren'py that allows you to put in characters "voices" (I call them chat sounds or text sounds) that's standard with Ren'py, doesn't take too much code-- I won't put it here since it's kind of annoying to have a bunch of code in the comment but if you want me to e-mail it to you or something I totally can.
Anyways, I use that code with a very simple method-- I find a "beep" or "blip" or whatever that I like, usually from a little beep machine (this one is fun: https://www.bfxr.net/ ) or from freesound.org -- I take it into Audacity and I make sure it's the length I want (usually you want something that's about a second or less? depending on how "fast" you want the characters to talk) and adjust the volume and little bit and viola!
Using the code I have it's just as simple as making a little beep .ogg or .mp3 and Ren'py does the rest for me. I've been doing it basically the same way since I started making VN's and it's always so fun to hear a new character make new beeps for the first time <3 <3 <3
I hope that helps! Don't be shy in asking me any questions and like I said-- I can e-mail you the code I use if you like!