Hi Tris, its all good questions because the more one looks at moon sowing dates, the more choices there are!
I understand two days before full moon as the date for most vigour, highest yield of anything, root, leaf and fruit – but not necesssarily the best quality. Two days before new, i.e. tomorrow, imparts least vigour. But also it is full-waning so the root part of a plant is favoured: good idea for mooli as they sometimes grow too big and watery.
Yes swede and turnip are roots, though the tuberous bit we eat is above ground. Its a root swelling.
For my part I just sowed on unfavourable days as I just needed to get them done eg lettuce sowing so I have plants ready to take over from the May sowing when it finishes. Also a problem for leaf veg is that there are so few leaf days compared with root and fruit, to do with constellation size I think.