I moved this to the #software:bahmni category. (Since the question is about Bahmni, it belongs here.)
You cannot use a Raspberry Pi as the server, as mentioned in this thread (which I know you already saw).
For the client, you really just need something that runs a modern web browser. I don’t know of anyone who has used a raspberry pi for this, but you could test it out and see. E.g. connect to the Bahmni demo server from that machine and see how it performs qualitatively.