I just got four baby Leucs myself about a month and a half ago. Mine have already grown a lot since I got them so you are unlikely going to be able to keep them in a 10 gallon for six months. Which means you're going to have to push up the finish date on that Exo Terra. I have the 36 inch Exo Terra as well and in is a great size for the Leucs...they're going to love it. As far as the backgrounds go there are a lot of options. Great Stuff will allow you to have depth and make ledges and plant holders. It is also lite weight. The clay method is very easy but is extremely heavy especially if you want to add depth. It is also the cheapest way to go. I personally think its too heavy for a tank that size...others may disagree. It also has to stay very moist or it will crack and fall apart. There are cork panels....tree fern panels...prefabbed backgrounds you can buy. You mentioned you didn't like the look of the eco earth...but there are a lot of ways to decorate it. I barely see my backgrounds as the plants, moss, and other things take over. Your tank is 24 tall so you'll want to come up with ways to help them use the height. They will climb like monsters when they are little but I have been told they are more terrestrial as adults. So I use wood to make slopes and tiered levels so they can easily get higher up. The 18 deep will give you plenty of room to do that. Then add in pieces of wood or a waterfall, along with a hillside, and plants and broms in the background you wont see the coco fiber. Also you can get some moss or creeping fig and it will cover it in and look green. The ABG mix is a great way to go and if you do the drainage layer like you mentioned and you wont have to change it out. Seed it with Springtails and isopods and you will have a balanced tank.