This doesn't mean every component has to come from the same supplier forever, once a setup is established and a keeper knows what works. But for a first setup in particular, where the cost of getting it wrong is a stressed animal and a return trip to sort it out, one supplier and one checked list tends to be the simpler route.
Whatever route a new keeper takes, the same principle holds: have the vivarium fully set up and running for a few days before the animal arrives, so temperatures and humidity have settled before anything moves in. A NRC Reptile Centre-experienced vet is the right point of contact for anything that looks off once the animal is home, rather than adjusting husbandry on guesswork.
Start with the enclosure. Size and material depend entirely on the species being kept, so it's worth checking a care sheet before buying anything else. Heating usually means a heat mat or a heat bulb paired with a thermostat, since an unregulated heat source is one of the more common ways an enclosure ends up too hot or too cold. Lighting needs vary by species too. Many reptiles need UVB provision to process calcium properly, while others need very little. Substrate should match the species' natural habitat and digging behaviour rather than be picked for how it looks in the tank.
Enclosure is the more general, catch-all term that avoids the debate entirely, and it's increasingly the word used in care guidance because it doesn't imply a specific style of build. A glass-fronted wooden cabinet, a mesh-sided setup for arboreal species, and a fully planted bioactive tank could all reasonably be called an enclosure, regardless of whether someone else in the hobby would call them a vivarium or a terrarium.
The rule of thumb worth keeping in mind is straightforward. If in doubt about husbandry, a care sheet and, where needed, a conversation with staff who handle these species day to day is the right first step. If in doubt about the animal's health, whether that's appetite, behaviour, weight, skin or anything else, the right step is a vet with genuine reptile experience, not a general practice unfamiliar with exotics, and not a forum thread.
A quiet room, away from heavy foot traffic, loud noise or other pets, helps the settling-in process considerably. Some reduced appetite or reduced activity in the first day or two is common and not automatically a concern, since travel and a new environment are stressful events for any animal.