Here is what I need help on. What is the best way to maintain running shape in the fewest sessions per week.

I just finished a marathon PR (2:49) and want to maintain most of that fitness while cutting way back on the # of runs per week.

I plan on one longish run session per week (10-13 miles) and then maybe one 5 miler and a brick run? Do I need the track/Tempo/fartlek?

Any thoughts on the best way to maintain. I have two halfs in june and july and one full planned for September? Thanks