Dual cores will work for basic stuff still and not feel too slow as long as one's expectations don't run away.
Hard to answer regarding Garage Band. I guess it wildly depends on how many instruments and tracks you usually end up with. Minecraft should run on a potato but then there's versions, mods and all that.
Regarding the 2015 to 2017 range only the 2017 models received official support for Ventura. The 2015 model runs Broadwell and the 2016 Skylake. Both technically support AVX2 and Metal 2 so Ventura runs fine so far on them through unofficial methods. I'd recommend the 2015 model even though it's a bit bulkier due to its proven reliability and no butterfly keyboard. I believe it's an uncontroversial take that the 2015 13" MBP was a pretty good model.
I wouldn't go with a 2015-2017 Air personally because I think the screen is a bit too sub-par, but to each their own. I don't think their performance is all that bad because the cooling system on the old Airs actually worked, so you didn't get weird ("within spec") throttles. But again, the screens...
Regarding RAM. This might matter in Garage Band, I'm not sure. For web-browsing, reading and media consumption, 8GB is still fine, but who knows for how much longer that sentiment will hold true. There were 16GB CTO options available for all of these models, though, so maybe if you stay on the lookout you could find one of them.