Leif
I started using modules last year like you and I successfully used them for:
Kale, Rocket, Spinach, Pak Choi, Chard (over-wintered and summer); Lettuce;
Beetroot (clumps); Onions (singles and clumps); Shallot (singles);
Pea (maincrop); Mange Tout; Runner Bean; Climbing Bean;
Sweetcorn;
Autumn Cabbage; Brussels Sprout; Spring Cabbage; Swede;
If you wanted to do carrot or parsnip, have you thought of using a 35 litre pot? I normally use them for growing potatoes or tomatoes, but they would easily be deep enough for you to be able to extract seedlings prior to them getting too big. I’ve successfully transplanted young carrots from rows where uneven germination took place, so I suspect that transplantation per se isn’t the issue, more root forking.
If you had soil deep enough like in a 35 litre pot, perhaps that wouldn’t be an issue either? I guess ultimately it depends on how many you want to transplant……