As @ghdprentice said.
I'd set up in there as you described, have a listen, and if possible get some measurements. With a REW sweep you could see what the clarity reverb times are in there at various frequencies. That will give you some idea of how much acoustic treatment will be needed in there.
It's a nice big space with reasonable dimensions. Does it have any support pillars? I have a similar sized garage with a support beam smack dab in the middle, which complicates any plans I might make for doing the same as you are thinking. It's partially drywalled, and there are a lot of things in there so it doesn't sound cavernous in there at all. Any empty space will tend to sound cavernous even if it isn't that big. If you have lots of shelves and some furniture and various items all over like I do it calms down pretty quickly.
Speaking of small reverberant spaces, I was up on the Cascades to Palouse trail this weekend. The outhouses along the way are basically bare walled concrete boxes. Small but amazingly reverberant, which is great for singing! There's also a 2 mile long unlit concrete tunnel to ride or walk through. Also quite reverberant and good for singing in the dark.