You’re doing great!
It’s basically all Cubes. Make each plank by itself, just like you already did. I’d model everything straight and then at the end bend it into shape with a Lattice Modifier.
You can use the Bisect Tool (under the Knife Tool) to cut the planks (make sure all the planks are selected!):

You can adjust the placing of the cutting plane with the yellow arrow and get it completely horizontal or vertical with the Plane Normal Settings:

With the planks that are in a corner, you’d need to cut the other end of the plank in half (CTRL+R) and connect the two ‘end middles’ with J:

Did this without looking at your reference, but the technique also applies there:

Should also be possible with a Boolean workflow, but that can be a lot harder to get right (it would be my first method to try, but if I couldn’t get it to work within a few minutes, I look for another method, there are many ways to do this…)
Hope this helps.