1. They will stay buried most of the time. My Kenyan, however, is pretty active and comes out (mostly in the evening). He's in a display tank and likes to climb his plants, his 3D rock wall background, his half log, etc. My Saharan is just as active as well; however, my Roughscaled is hardly out.
2. A lot of people used aspen. I use crushed walnut shells for my Kenyan currently and aspen chips for my other sand boas. I'll probably switch to aspen chips for my Kenyan when I'm out of crushed walnut shells. I've heard of some using sand, but others say it's too heavy and difficult to clean.
3. When I take mine out, I try to come from the side/bottom as to not startle them too much. They will usually try to flatten out making it a bit more difficult, but they've never gotten aggressive, etc. They're pretty laid back.
4. 20L would be great!
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1.0 Ball Python "Aragorn"
1.0 Bredl's Carpet Python "Strider"
1.0 Kenyan Sand Boa "Gimli"
1.0 Saharan Sand Boa "Frodo"
0.1 Rough-Scale Sand Boa "Arwen"
1.0 San Felipe Rosy Boa "Legalos"
0.1 California Kingsnake "Gentoo"
1.0 Mexican Black Kingsnake "Indigo"
1.0 Snow Corn snake "Chile"
0.1 Okeetee Corn snake "Amazon"
1.0 Crested Gecko "Willow"
0.0.1 Irian Jaya BlueTongued Skink
0.1 Australian Cattle Dog/Pointer "Kira"