I saw this sentence format a lot before like "who am I to~," but what's it mean and in what context can I use this format?

I've heard "made up of" can be used when something is a mixture of more than three things. Is that right?

Yes, that's right! Something can be "made up of" many things or people. Not just one or two things! Ex: The team is made up of seven members. Ex: The meal tonight is made up of five courses.

What does "time on [someone]'s hand" mean? Is it a common expression?

Yes, it's a common expression. It simply means that one has time; they are not busy. Ex: I can help you out with moving this weekend. I have lots of time on my hands recently. Ex: Work has been very busy recently, so I don't have a lot of time on my hands.

Is "surprisingly" different from "surprise"?

"Surprisingly" is the adverb related to the word "surprise." It means unexpectedly, or in a way causing surprise. The speaker has used "surprisingly" to warn against paying medical bills that are unexpectedly high. Ex: Surprisingly, the food at the restaurant was better than expected. Ex: The student did not get in trouble for skipping school, surprisingly.

What does "bedding" mean? Does it refer to hay?

"Bedding" is basically any material that is used to sleep on or in. For humans, bedding usually refers to bed sheets, blankets (also called comforters or duvets), and so on. For animals, like the hamster in this video, it can be straw, hay, or even shredded paper. Ex: I need to change the bedding in the hamster cage. Ex: I bought new bedding for my room. It's super fluffy and warm, so I love it.

What's "show up" mean and is it different from just saying "show?"

"Show up" is different from "show!" "Show up" is a phrasal verb that means to arrive somewhere to join a group of people or for an event or gathering. Usually unexpectedly or quite late. "Show" means to allow or cause something to be visible or a stage performance. Ex: Our dinner guests didn't show up last night. So after an hour we just ate the food ourselves. Ex: Josh showed up to watch our dance rehearsals. => unexpected Ex: We went to the eight o'clock show. The performance was magnificent.