You will want to try to get the bubbles out of the tank without breaking them. They are an algae that can take over an is unsightly.
The xenia, you can peal them off the rock. cutting them with scissors will be a mess. And nothing is going to eat them.
The leathers, yeah, glue does not stick to them but if there is any rock rubble or sand attached to them, the glue will stick to that.
otherwise, you can use a needle and a heavy thread and actually run the needle and thread thru the leather and then around a piece of rubble rock. Do that 3 or 4 times to hold it to the rock and it will attach itself over time. You can cut the thread later and pull it out. The leather will heal over, and you will never know you put holes in it.
API test kit can be hard to read. It goes bad sooner than its dated for too. IMO. When they are new and you are testing for the basic ammonia, nitrates & nitrites and pH, the kit isnt too bad, but once they are opened they dont last long. They are not real accurate on the nitrates either. They will read 0 when you actually have up to 10-15ppm. Thats been my experience at least.