For a full multimodal routing engine including realtime data for transit, you should have a look at OpenTripPlanner version 2 (if you haven't already): https://www.opentripplanner.org/
For a single solution to geocoding and autocompletion, there's Pelias: https://pelias.io/
Pelias is pretty difficult to use with the kind of automated config I'm hoping to have for this project but I might give it another go.
OTP is actually really fantastic and it might be a better choice than valhalla's multimodal especially if it can handle GTFS realtime. Thank you for the reminder that it exists!!!
For a single solution to geocoding and autocompletion, there's Pelias: https://pelias.io/