I've made a reasonable start on April with a 15km road run in my old flat shoes; the red ones are sidelined for a while and might appear on eBay soon (there are a couple of slightly used pairs of similar shoes). I made a point of running at a fairly comfortable pace and adapting my gait / foot position if I felt any niggles. I also did not look at the GPS to check pace although I did peek at it twice to see how much more i had to go!
The result was a credible 15km at a 5:01min/km pace which is as good as it'll get at present. At the end my legs felt pretty tired, and not just my knees.
Today, things felt OK as I walked in and pottering around work hasn't been painful but I am aware of the legs more than I should be. I'll find out a bit more at the circuits later, but I will avoid deep squats and lunges. I will try a few shallow ones but will stop if there is are any 'Ouch' moments.