When the RouteFinder sees a new IP from the ISP (pppoe), does the dynamic IP client do an update immediately after? It seems like there is a good size delay. Does this cause a delay in the IPSec connection?

Yes, when the RouteFinder gets a new IP address on the WAN link, the DDNS client will update. It might take a few minutes. The IPSec connection will definitely have some delays when there are IP address changes on the WAN link.