Hi.
You can indeed expand the number of analog inputs up to 64 via the Analog Multiplexer add-on for Bela that we sell in our shop: https://shop.bela.io/bela-accessories/bela-mux-capelet.
Keep in mind that multiplying the number of analog ins comes with the cost of a lower sampling rate (copying from the shop):
When you use the Mux Capelet the Bela software will automatically cycle through all the inputs, giving you 2.75kHz sample rate (22.05kHz / 8) on each of the 64 inputs. Alternatively, you can use 32 channels at 5.5kHz or 16 channels at 11kHz.