I think it's safe to say, we've seen everything there is to see about Reapers. It's possible that they are instigators for the whole Andromeda exodus, but I doubt there will be a connection beside that. At least I surely hope there isn't.
As for similarities between the design of Citadel and Arks. Yeah, there is to a some degree, but I highly doubt it's due Reaper influence, but I'd wager both just use the centrifugal force, thus similar shape and structure. I've always wondered why this quite simple and cost-effective way to maintain artificial gravity seems to be so rarely used in the ME universe (ofc, unless those Arks are 1km dreadnoughts it will be lower than let's say Earth's gravity. I reckon less will do when conserving energy is somewhat an issue on 2.5 million light-year long journey).