Getting a bigger terrarium…

Finally upgrading out gecko into a 18x18x36 and was hoping to get some advice from a more experienced owner, might be a silly question do I need a bigger light now since the tank is upgrading or should my reptisun 13 Watt 5.0 UVB still be good? Also where can I find a cork bark background for the tank? Can’t seem to find one the correct size online any other tips or suggestions would be much appreciated thank you so much