If you could post a pic of the deck area in question, that would help with opinions. There are a number of folks who have built their coops/runs under a deck with success. Try searching the forums for those and compare with the area you have.
Evaluate the area - does it get or stay damp/wet - if it does, then IMO look for another location. If it stays dry then you can make it work. Sand IMO is the best option - easy to clean by sifting or raking - add a little PDZ if an area does get a water spill from the fount or rain. But sand doesn't work for all locations - and a deep litter bedding will be more difficult to manage under the deck.
Also the location of the deck can help you decide - you need at least some sun part of the day to reach the run to help keep it dry and an area for dust bathing.
If you cannot stand up comfortably, then cleaning chores will be a real pain in the back.
How often to clean will depend on how many are in the flock - I personally clean my coop/run weekly and often scoop poop in the coop more often.
glad you have joined us. You should post an intro under New Members forum to get a proper welcoming.