Sometimes I forget that not everyone is "Hands On" when it comes to maintenance, let alone construction. If you're hiring contractors, you need to screen them, and find someone who understands the construction techniques that are unique to sound isolation. I have a neighbor who built a large room addition specifically to serve as a recording studio and rehearsal space, and his greatest obstacle was getting his highly skilled and experienced contractor to build to recording studio specifications, and not living room/game room standards. (I was already well into constructing my own when I learned of his project and understood exactly what he was up against. Like me, he had done his research. He knew what he wanted and knew what needed to be done, but had a difficult time getting contractors to understand how he wanted his room built, and why)
I think the best resource for you is Rod Gervais' book https://www.amazon.com/Home-Recording-Studio-Build-Like/dp/143545717X You can probably find it at your local library. It's the kind of thing that will cause your eyes to glaze over with its highly technical detail, but you'll find answers to questions you didn't even know you had. And... it can help you with understanding all the ventilation and air conditioning options you have that will work with your particular situation.
There are many on-line resources to help you understand what you'll need to design your space. (There are lots of worthless youTube videos that will waste your time, and feed you misinformation. And others that are invaluable in helping you make decisions) Read Rod's book first. Then you'll be better armed to understand what advice to pay attention to, and what video's (Or on line discussions) to ignore. You can follow threads on GearSlutz https://www.gearslutz.com/board/studio-building-acoustics/ and from there you will find additional resources that can help with your build.
The space I started in had only three sheets of drywall installed, covering older fiberglass insulation that was industry standard when installed between the living room wall of an apartment, and the garage. It was a "no-brainer" to remove those few sheets of drywall, and insulation at the beginning of my project. I used 120 sheets of 3/4" drywall in my project, and like you, I did it in a single car garage. There's a lot more than drywall that went into my project. I "finished" the existing space, and then framed an entire room inside that room, and "Finished" it. (Think of a Box, inside a Box, with a 1/2" airspace all the way around).
You might want to consider consulting with George Whittam. He's in your area, and has designed studios for professionals all over the world. https://about.me/george_whittam He's got weekly webcasts specific to the voiceover recording process itself, and is an invaluable resource in building new studios and tuning existing spaces.
If you've got the space, and you've got the funds, I'd build a nice big roomy studio right there in your garage. It will let you play by yourself or with friends without disturbing your neighbors or your guests. And, after you've been hosting for a number of years you'll appreciate that it doubles as a private sanctuary, allowing you to escape from your guests into a world of your own, where no one can disturb you.
