- What is the difference between the total bitcoin amount sent and the transaction size? I thought they were one in the same.
"Size" in this context refers to the amount of data (in kilobytes) required to encode the transaction.
- Maybe a receiving fee or a fee for maintaining wallet for xx days with no transaction may be in order.
A "receiving fee" can't work because the receiver isn't necessarily online at the time the transaction is made. A fee for "maintaining" a wallet makes no sense, since wallets require no maintenance. In fact, until coins are actually sent from a wallet, no data about the wallet even exists in the network. Sending transactions and confirming them is the only thing that requires actual resources, and this is what fees are charged for. The fees are paid by the sender (who consumes the resources in question) to the miner (who supplies the resources to confirm the transaction). This is the fairest way of doing it.
- What stops someone from doing a bloat attack, where they make lots of small (or large)transactions to themselves, increasing the size of the blockchain?
Transaction fees. Since sending transactions to yourself repeatedly requires a transaction fee each time, anyone who attempts this will eventually run of money. By paying transaction fees, you are essentially purchasing the right to add data to the blockchain. Since fees are paid to the miners, and miners are the only people who really
need to process the blockchain, there's no problem. If bloat becomes a problem for miners, they can simply increase their fees until the revenue from fees is greater than the cost of dealing with blockchain bloat.
Another person wrote using Electrum or other client that hosts the blockchain separately. I may very well have to do this in a few months. Too bad everyday people will not be able to host their own node. We will have to rely on 3rd parties. Some consolidation is natural for 'on-demand' services, but doesn't this defeat one of the original goals of bitcoin, which is to make it accessible to masses with decentralized authority? If pruning will not allow significant re-use of disk space, the blockchain that is the the very heart of the bitcoin network will have to be placed into the hands of trusted 3rd parties to get any practical use out of it.
Nobody "has to" rely on third parties. People can
choose to rely on third parties if they find it cheaper or more convenient, but anyone who wants the security of a full node is perfectly free to run one at their own expense. Remember, that's "free" as in speech, not as in beer. The security requirements for a digital payment system are massive, and absolutely cannot be provided at no cost. Storing the complete history of every transaction may seem inefficient and expensive, but it is the only way to provide the required level of security in a decentralised system. Your complaints sound like someone who refuses to use a safe deposit box because they don't trust banks, then complains that installing a vault in their basement is too expensive and takes up too much space. Ultimately, you have to either trust a third party to provide security for you or else provide security for yourself at your own expense, because you can't get security for free.