I've bitten off a pretty big spring/summer season:
on May 1st
Relay team entry into the Sinister 7
on July 9/10.
I'll be running leg 5 for the relay, which consists of ~30km of trails with 2500" of elevation gain.
I think my endurance will be good after training for the marathon, so I'll most likely take a week off of running then hit some event-specific training up until the relay.
Another option that I'm contemplating is signing up for a 10k trail clinic in March, helping build strength for the marathon while leaving my Sundays open for long runs.