That playpen doesn't look high enough. If you already have a cage for him, I would suggest instead, to get an xpen that is 30 inches tall at least, though you may want to go 36 inches if you want to play it safe. You can try 24 inches, but there's a chance it won't contain your bun, then you'll have to buy something taller. An xpen will be cheaper and will also give you more space and more flexibility on how you can configure it. There are also ones available with a door in one of the panels.
Xpen for pets, 30 inch
If you're having issues litter box training him, these links have some good info on litter box set ups. It can also be hormones. So once he's old enough to neuter, that will help as well.
https://rabbitsindoors.weebly.com/litter-training.html
http://wabbitwiki.com/wiki/Litter_training