Hi and welcome to the forum!
You can buy online, you normally get a better deal if you do. Lucky reptile and exo terra terarriums work well because they are available in good sizes (45x45x60cm for adult Cresties) and have a mesh top which you can put a light on top of so you can view at night if you wish. The mesh top helps with ventelation as well.
What are the temps of the room the Crestie would be in? Day time temps should be between 72 and 78 ideally so quite often room temp is ok and no additional heating is needed. If you do need to use a form of heating then a heat mat is good, you can stick it on the side but make sure its on a thermostat otherwise it could get too hot quite quickly.
It is a good idea to have the viv set up before getting the Crestie just so you can have stable temps and humidity for when he/she arrives home
