i got my hatchie of a similar species not too long ago
i housed mine in a 12L click clack until he was 7 months, weather you can house all three in the one i'm not sure. DO NOT USE SUBSTRATE! at this age a couple grains of sand is all it takes to cause impaction as for papaer towel on the bottom i found that crickets hide way too well under this. i already had my adult cage when i brought mine so i put the click clack inside the tank and used the red light bulb to heat the click clack with a probe hermostat with the probe inside the conatiner obviously. you shouls try and maintan the temp at around 30 and the humdity at 40 -50 so you don't get problems with sheding.
although its very temting to put them straight in the big boys tanks do not do it you;ll have way too much trouble with them not being able to ctach their food, most poeple wait till they're between 6 and 12 months before the move. after the move you can use sand, i do and haven't had a problem mainy becuase i feed roaches that mine catchs on the walls far away from sand.
in terms of plants these guys can live in arid environments so living plants may not be natural, i have a couple of fakes in mine, but my guy ignores them , he loves his logs and branches though.
hope that helps