It's all useful information.
Yeah, right now I just want to record acoustic guitar and vocals, but I can foresee wanting to add drums or drum loops and bass eventually.
I hate my Windows PC so I might have to go and get myself a Mac with Thunderbolt 3. I figure I'll never wish I had more latency.
So, adding vocals to the mix, you'll need something with a mic pre, an instrument input, a Lightning adapter and compatible with iOS Garageband (for the bass and drum loops).
If it were me, I'd be looking at something like this: Behringer iS202 All the ins and outs you'll need for an iPad recording deck.
Focusrite had the iTrack dock, but seems its discontinued. Maybe look for a used one? I use the older Alesis version with the Gen1 iPad...just as an easy scratchpad for ideas.