I think the muscle loss is pretty overrated. If you stay under 20 miles a week and continue doing some lifting I doubt you'll see much muscle or strength loss unless you're an elite lifter.
I'd say start with 1-2 intervals and 1-2 tempo runs per week. Every second or third week replace 1 of the tempo runs with a longer run starting with 3-4 and working up to maybe 9-10 mlies. You could probably add this on top of whatever you're doing now. You have plenty of time so you can build up slowly. For intervals I like doing some longer intervals instead of all the tabata type stuff in CFE.
Do you have a goal time? What can you run a 5k in? What do your workouts look like now?