I make similar, but on hormones!
I'm using homemade corner brackets to hold the 4 sides together - 8 per bed and I've got two of these large beds built. The level is 3 feet, so the side walls are a bit over 6 ft. A local shop gets a limited number of pallets that length by 30 inches tall which is a lovely working height if you're getting a little older...
Places where I have used pallets for beds and *not* filled in all of the cracks, I've had a greater tendency for rats to move in, so I think it's worth it.
If you're in a spot with lots of freeze/thaw cycles +/- a lot of rain, I would consider putting some sort of a strap/rope around the top for extra support from the outward pressure.
If you're filling it with lots of wood, expect the soil level to drop a lot the first year, and lesser amounts subsequent years. True hugel beds do that also, although the better you pack soil around the branches, the less trouble that will be. At least one of my beds ended up with too much organic matter, and as I was topping it up, I added thin layers of fairly clay soil and some homemade biochar.
One of the beds like the picture, currently has kale and green onions growing (not fast due to low light, but better than nothing). The second one needs work done on it. I covered it in plastic during an early freeze to try to get a few more cucumbers and hope that a pumpkin that was formed to ripen. There are still bean plants that will have some seed on them, so I need to collect the seed, chop and drop most of what's left, and then cover with leaves for the winter. The pumpkin's on the kitchen counter - not sure it's far enough along to be anything more than chicken feed, but I tried!