Those are not really specific questions. But I will try my best to somehow provide useful information.
> 1. Energy efficiency of the transactions and the network
If by "transaction" you mean a single economic exchange between two agents, then the energy cost of a single transaction is impossible to measure. Many of the on-chain transactions in Bitcoin today are "batched" to reduce their total size thus saving on fees. Each of these batched on-chain transactions can easily represent dozens of individual economic exchanges. Lightning Network (LN) takes this even further with bi-directional payment channels now representing potentially tens of thousands of transactions over the lifetime of a single channel. It requires one on-chain Bitcoin transaction to "open" a bi-directional payment channel, and another transaction to "close" it. Closing is not strictly necessary and will be less so as infrastructure and tooling improves.
Bitcoin is not really one single network. It is a few different networks operating in their own niche with their own specific optimizations. Miners can operate as dumb hashing computers with no visibility or knowledge about the blockchain other than the next chunk of data to hash. Full-nodes are typically operated by the "users" that wish to carry on the mantra of "don't trust, verify"; value their personal privacy; or are a large commercial entity. The last estimates that I saw were about 10,000 publicly reachable full-nodes and another 100,000 private or non-reachable. There are also mobile wallets that can be custodial or "light clients". Then the Lightning Network (LN), which consists of public and private nodes, mobile and custodial apps, nodes backed by full-nodes and LN's version of light clients.
> 2. How democratic the process to mine new coins is.
Mining appears much more centralized than it is - due to the success of mining pools. Mining pool operators do not control all the hash power that congregates in their pool. Instead the owners of mining rigs/operators can point their rigs at the mining pool that offers them the best ROI. Of course sometimes other reasons override the profit motive but usually only temporarily - see the SegWit political / governance drama from a few years ago. Corporations (and governments) have already started investing in mining equipment in an effort to secure their own interests in the space. They will compete with each other here just as they have competed with each other over territory and natural resources for hundreds of years.
> 3. What steps are taken to manage frauds, speculations bubbles etc. to protect malicious actors from gaming the system.
Bitcoin is governed today by the same laws and rules as other systems. Fraud is fraud is fraud. Criminals, scammers, and fraudsters use banks and cash too. From the sound of it, you would prefer to err on the side of institutions and regulation. I disagree, and would prefer that individuals take personal responsibility for their own education and finances. The world is a messy place and there is no answer for 100% of the people 100% of the time.