Questions about how Ethereum works

Just read Preethi Kasireddy's paper on how Ethereum works. Great deep dive article. But have a few questions after reading the article. Would appreciate if anyone can help me fill in the gaps or point me to another paper that covers my questions but is non-dev friendly :).

1) Each block has a state trie. However, does the state trie include the current state of all Ethereum accounts or only the states of accounts that are updated during the current block?

2) if a node wants to verify a transaction, it can do a Merkle proof. But to do so it needs the branch of partner hashes leading up to the root. If it is a light node, where does it get all the branch data? Is it possible? Or is Merkle proof only feasible for full nodes?

3) when a miner mines a block, do the other nodes/miners validate the transactions in the block or just accept them?

Thanks!