If you have the means, i'd personally recommend starting with a PVC enclosure like Animal Plastics if you have the means to do it. The enclosure is big enough for a BP for the rest of their life and it will make it easier on you to keep humidity and heat at the right levels. Most importantly, you'll buy everything once and won't have to repurchase anything.
You can always purchase a divider for the PVC terrarium so it doesn't overwhelm a small BP and then remove it once it has grown.
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