The first confirmation occurs when a transaction is included in a block.
When another block is built, no mention is made of that transaction, but there is a link to the previous block. This block is the 2nd confirmation.
The transaction size depends on how many inputs and outputs it has. In general each input is the same size, no matter how much it is worth.
The transactions are released cryptographically. There is some computation used for this, but that amount of computation is negligible. Compare it with the effort to sign a check, compared with the subsequent handling of that check.
The situation with dust is analogous to writing checks for $0.000 000 054. Such a check consumes paper worth more than the amount paid. It is a pesky nuisance.
Of course, we don't do that. I don't know if there was minimum check size in Zimbabwe, but imagine writing a check for 1 Zimbabwe dollar. Or imagine a merchant who has some griefer who always pays in boxes of Zimbabwe dollar bills.
