1. You have plenty of time at DTW - from C you will go down an escalator to the psychedelic tunnel and walk/ride on moving floor to another set of escalators to A.
2. As of 1/15 DL will no longer interline baggage, so if your DL & AS flights are not on the same PNR (separate tickets) you will have to pick up your baggage in Seattle & recheck it.
3. You should be able to check in for your DL flights 24hrs. ahead of time, & then the AS flight 24 hrs. ahead of that departure (assuming they are not on the same PNR).