What should I use at the bottom of the cage?I believe you have a little boy but to confirm try to get a pic from the side with baby gripping a branch.
So there is a lot you will want to change on your set up. All the bark needs to come out. It is an impaction risk and will just grow bacteria and mold.
All fake plants you will want to remove. You can hook them to the outside if you would like to add coverage but inside they are a risk because veileds eat their plants.
You can get that live plant higher in the cage by flipping a pot upside down and putting the plant on that.
Looks like one of the vines is the exo terra jungle vine... If it is it would have like a black sand texture to it. This one would need to be removed. They are dangerous for their eyes if they rub their face on them.
This is an excellent link on all the basics. And it walks you through everything including cage set up.