Since you are not talking about Bitcoin, but you are talking about all cryptocurrencies including centralized coins, I would like to point out something.
cryptocurrencies are independent of any central entity and operate on a decentralized network, so their value is based on supply and demand in the markets and their use for the execution of transactions.
Not all cryptocurrencies are decentralized. Most of them are centralized and could be controlled by their devs. There are 1.8 million crypto based on Coinmarketcap, and 1.79 million are centralized. The developer team holds the maximum shares of the total supply they will use against their holder once people start investing in it.
3. How is the value of a cryptocurrency determined and how can it vary in the market?
Each cryptocurrency has a limited supply, meaning its value can be influenced by the amount of demand for it.
Not true. Half of the cryptocurrencies do not have any supply limit. ETH is an example. ETH moved from POW to POS, which has no maximum supply limit. So, it's not decentralized. However, ETC (Ethereum Classic) has the maximum supply limit. I do not trust any coin that does not have a maximum supply limit.