I had to look up hugelkulture... Wow! That looks pretty neat, but definitely a multiyear process. It will take a lot of bulk to get the moisture retention you are looking for and will always still need to be watered. I would watch the wind and sun directions when orienting the berms.
The problem with a wicking bed is that the gravel tends to get clogged with debris/roots over time. This reduces the ability of the water to flow and creates dry spots.
I would advise building your 24" bed and then laying in drip irrigation on top. With a dripper right up under each plant, there are fewer weeds and less evaporation. You can also mulch around the plants to reduce evaporation, but make sure you are mulching around the plants and not on their trunks. The one problem with mulch is that it sometimes leads to bug problems, so you might just go with drippers first and see how the plants do. I lived in southeast Idaho, and drip irrigation tended to work fine for my veggie garden.