I would replace the pellets with something that holds humidity better and does not get moldy. I use shredded coco coir, its a bit messy but it hold humidity extremely well.
I am planning on replacing them with something different, there were just what i was recommended in a shop, but it's hard to choose when everyone gives different advise...
I use soil for the base because its cheap/free and coco coir for the top layer. For the base of my enclosure I laid plastic sheet across the bottom so I could just poor water into the enclosure without it leaking or rotting the wood and keep the humidity up. I like my substrate a lot because it was cheap, easy to clean, and I can grow live plants and seeds in it. Whatever you choose I would just try to keep it as "natural" as you can..
Looks great! you could also use chemical/pesticide free potting soil that's what I use, it's like 2 dollars a bag where I live and super easy to plant things in and holds moisture pretty well
Other people here know way more about substrate than I do, but I have an important question: is that a picture of a tort stuck on the inside wall? If so this is the cutest enclosure of all time.
Hahahaa, there's a sign which my friend bought from Germany about a tortoise, and a picture of a tortoise catching a frizbee, and thanks for the advise guys, i think i'll get some coco coir if this many people recommend it!