Many blocks are faster than 10 minutes. As a matter of fact, more than half of the blocks solved are solved in less than 10 minutes.
Correct, the difficulty is adjusted every 2,016 blocks to bring the AVERAGE time between blocks as close to 10 minutes as possible. This is the speed of blocks, not the speed of transactions. Transactions have many different speeds, depending on what you are trying to accomplish. There is the time to create a transaction, the time to broadcast a transaction, the time for a transaction to be relayed throughout the majority of nodes, the time for the first confirmation, the time until the recipient is willing to release whatever is being exchanged, and the time until most people feel confident that the block containing the transaction won't be replaced.
Nodes are already decentralized. That has no effect on the time for blocks to be solved and has minimal effect on the time for transactions to be relayed. Since nodes are already decentralized without a pool, why do you want a pool? Who would participate in the pool, and why? What benefit would come from a pool of nodes in place of individual nodes?
Perhaps you mean pool of miners instead of pool of nodes? Those already exist. This allows those supplying hashpower to work together on solving a block, and then share the rewards from the block. That way their is less volatility in frequency and value of earnings from hashing. This has no effect on the frequency of blocks nor the speed of transactions globally.
Maybe. Depeends on what you are trying to accomplish, and why you think a pool is the appropriate solution.