You are suggesting that I use an USB stick rather than an SD card, and thanks for that observation. USB sticks are easier to use and to store, so that looks to be the option to use. Can you see any problems in keeping the blockchain on a USB stick? Would it be better to run a full node rather than a pruned node?
Your terminology could be corrected to stop misconceptions spreading:
Pruned nodes are full nodes. The 'full' in full node refers to that the node fully verifies all the rules of bitcoin.
Nodes which store the entire blockchain on disk as opposed to pruning can be called 'archival nodes'.
As for your project, I run a similar one on a notebook laptop which is always-on. I installed ubuntu, uninstalled the desktop environment and only control it using the terminal or ssh. Be prepared to wait some time to sync the blockchain from the beginning, but once you're done it will use barely any power, bandwidth or CPU time.
One possibility is to enable pruning and sync the blockchain on another faster computer. Switch off bitcoind and then copy over the ~/.bitcoin/ directory to your notebook, when it starts up it will not need to sync.
I am aware of 3rd party wallets, but don't wish to use them. I prefer to control things via a core wallet. The transactions that I hope to make will include cash purchases of Bitcoin, and the sale and purchase of domain names.
If this is your use case, have you considered running an always-on full node at home, and then pointing your lightweight wallet to connect only to it. That way you'd get the full privacy, security and trustlessness benefits of a full node but without having the potentially long startup time.