Cover crop on hugel bed

I'm planning on building a long hugelbed that will double as a swale. I'm going to be planting a lot of annual vegetables in it and some perennials as well.

I have read info about the wood decay in the beds locking up nitrogen (during early phases), which makes sense to me. I'm looking to ensure it doesn't become an issue to my crop that will be planted within two months of the bed's creation (I can't wait longer). My ideas are to plant a cover crop, and mix in a lot of coffee grounds to the soil that is mounded over the wood (I've been collecting pounds and pounds of used coffee grounds from local coffee shops in prep for this).

I'd like to get your feedback on the coffee idea, as well as the idea of planting a lot of red clover and buckwheat as an early cover crop that I would chop and drop as the annual vegetables start to take off (the idea being that the clover would add nitrogen, and buckwheat act as an insectary, and both would stabilize the soil with their roots). My only concern with the cover crops is that I once planted squash (something I'm focusing on this year) in an area I also planted clover, and I could NOT keep up on the clover chopping. The squash vines got all tangled in it, making it impossible for me to chop much of the clover without damaging the squash vines, and what I would chop would just grow right back quickly. The clover also held a lot of humiditiy and moisture around the squash leaves which I think caused them to get a fungal disease of some sort that ended up killing the squash. Also gave the squash bugs a nice place to hide.

Any input would be appreciated, thank you!

How about winter rye as a quick growing cover? In your zone it will die on it's own once the weather gets hot, leaving the root system to decay in the bed and I like the tops (the grass) for a fresh green mulch around the plants. Fresh green grass clippings are my favorite mulch.

As for the fungus, here in zone 7b/8a I have always fought fungus and mildew no matter what I did. I used a chamomile tea spray daily. It did a pretty good job but if I started missing days the fungus would take over.

coffee grounds are an extremely potent source of nitrogen. Often too potent. Mix those grounds with some dried leaves or dry brown a few weeks before using them. It will produce real compost.