you can get kits which are no fuss. I did that for mine.
Corrugated iron sections work and are cheap if you're doing a lot.
If you are set on wood, and let's be honest it's gorgeous, you could just screw the wood together in butt joints. No need for corner posts, once it's full of tonnes of dirt it won't move. you probably want to treat the wood or choose one that's rot resistant. TBH I just use a mix of pine tar and linseed oil on all my outdoor construction as it looks nice, is cheap, and won't permanently poison the land.
Plan to have fittings for netting. I use PVC pipes with elbow joints bracketed to the side. You could also drive steel fence posts into the ground and slip pipe sections over that. I string insect netting over the pipes, it has grommets which fit onto screws in the side. Fewer problems with pests, maybe you have to do hand pollination but usually wind and ants are enough for me.
Irrigation is easiest to do when installing the beds if you want to do that.