I'm fascinated by the fact that we can set the fee. Suppose I set it to the minimum (or zero...?) is the transaction guarenteed to go through (with the delay)? Thanks.
The minimum fee you can set is 1 sat/byte.
please note that 1 satoshi/byte is the minimum fee that you can set when using a wallet, and minimum fee that 99% of the nodes and miners have set in their minrelayfee which means they would reject any less than that.
but at protocol level the actual minimum fee is zero which means sending the entire amount.