Hello Dan, your chicory plants should be fine as singles or clumps so it depends whether you want smaller or larger leaves. It is more fiddly to pick leaves from clumps but I find the yield is slightly higher.
I have the same question about Pak Choi. I sowed 3 or 4 seeds per module (as they are an oriental vegetable) at the beginning of the month. They grew very fast and are now very leggy. I was considering pricking them out singly into other modules…
Good idea as pricking them out allows you to bury the stems and make them more sturdy. Then as single plants, it means you have fewer but larger leaves, so if they are for salad you could plant them closer (say 15cm) or 25cm for large leaves.