Maybe the better question is: what hardware is best for someone looking into using lightning and developing with it? but that's ONLY what the hardware will be for...and then also, what hardware is needed to manage a high volume of small transactions?
Discussion
people are so busy answering the question of 'how to run a lightning node' there isn't a lot of answering of 'how to have a great lightning setup'
That's going to be beyond the scope of my knowledge, since I am not a dev. I would not have a very good idea of what would be the ideal setup for someone focused on that single use-case.
I don't think there are going to be any hardware constraints for handling a high volume of small lightning transactions, though. Transactions on lightning don't have much data footprint to speak of, unlike on-chain. This is because on-chain you have to keep a copy of EVERYONE's transaction data, not just your own, while lightning you are only concerned with the updates to your own channel states.
I have yet to find any good information on figuring out power consumption of various computer systems.
Best I seem to find is just people recording results like this
https://community.start9.com/t/start9-server-power-consumption/180
hard to make sense of that being comparable to a r-pi. would think considering they don't use ARM chips that it's more expensive...also utilization of more ram seems like it'd be more expensive. Trying to learn more, still haven't found good resources.