Hi :)
I think this part is very unlikely: Banks are a thing of the past because most people (hard bitcoiners now) prefer to keep their coins with their own private keys, being their own banks.
  1. There will be custodians, because some people and companies will still need them. I don't think they will be lenders though, unless they will act as a intermediary between the bitcoiners looking for yield and the borrowers.
  2. There will be entities owning large sums of money, willing to lend it – banks and non-banks (eg. companies with cash surplus).
  3. The smart contracts will be a natural way of sorting things out.
  4. In a sound money environment the growth will be indeed slower than now, but without the extreme boom and bust cycles – and it's good. It will be calmer, less greedy and more natural. The sound money provides better life for everyone, so the incentive for high-yield, high-risk ventures will be less. But there always be people wanting more and they will find ways to finance it.
IMHO.