Hello Simon and welcome to the forum :happy:
I think you've got a good start! My only suggestion would be to add another hidey hole or two or add some plants for your little fellow to hide in.
The rocks are beautiful. Where did you get them? If they are from the outdoors, be sure to keep an eye on pH, hardness, alkalinity, etc for a few days to make sure they won't impact water chemistry (I speak from personal experience
![Big grin :D :D](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
).
Also, large rocks can make cleaning the aquarium a little more difficult as opposed to a sand substrate or no substrate at all since food and detrius are likely to sink between/beneath them. But as long as you keep this in mind when you syphon out your tank there should be no problem.
Some kind of food dish might be helpful for clean-up as well.
I've never thought having a rock substrate was much of a problem or hastle once I got used to getting the syphon around them and, personally, I think it looks better than sand. I've also heard that gravel and rocks are better for beneficial bacteria to cling on to than sand.
Anywho, there are a lot of great/knowledgeable people here who can probably give more input, but from the looks of it, I'd say your little guy is going to be quite happy :happy:
Good luck!