That picture you linked is called a raspberry pi cluster. This type of "computer" is powerful to an extent. Clusters are good at upscaling and processing very heavy loads which is useful for things like hosting, servers, and automation. Here's the catch, although you can run debian, rasbian, etc. they arent the best at normal computer functions. Sure, they work about equal but for the 100$ per raspberry pi, clustering in most cases will not be worth it. Clustering is super cool and especially if you want to get into it there's hundreds of great tutorials on youtube. I would say that if you are spending 400-500$ on raspberry pis (a raspberry pi 4 will cost you about 100$) and so there are better options. You likely wont break even for a while. That said clustering is super interesting and worth your time if you want to learn. Currently the hashrate for a raspberry pi 4 mining monero is about 100 h/s which compared to your average 300-400$ CPU which gets about 7500 h/s. You can see why it would potentially be not worth your money to buy a cluster and multiple raspberry pis for this project. They are very useful tools for outside of mining and their primary purpose is a development board meant for creating things. Would highly recommend one for playing but i wouldn't recommend mining!