How to take care of my deck for extended periods of no use?
I'm not a hardcore gamer, so I probably get a few hours of deck time a month.
Between long periods of no use, is it better to leave it plugged in and charged, or is it better to let it run out of battery and stay discharged for extended periods?
Either 100% or 0% is not very good for a lithium-ion battery. Around 50% is usually best, so I'd aim for that. If you aren't going to use it for long time, charge it to around 50% and put it in battery storage mode.
A recent update added the option to limit the deck's max battery charge in Settings>Power. If you want the deck to be ready to go, I would recommend capping the max charge at 60-80% and leaving the Deck plugged in. Alternatively you can put the deck in battery storage mode.