[lxgr]

I'm using a Model 4 with 4GB of RAM, but 2GB would probably also be ok. (I haven't measured peak memory usage, but I imagine that having some spare memory for file caching reduces read contention for the SD.)

Home Assistant can take a minute or two to start up, keeping all four cores quite busy, so I wouldn't recommend trying this on an older model myself.

If you want to use the Pi's internal Bluetooth module, obviously you'll also need one that has one and supports Bluetooth LE. Again, I can only speak for the Model 4 here, which works great for that.