Good to have the beds built! I can see carrot envy coming on if your soil is as sandy as that
Anything organic is going to help... if you are going to grow runners or other beans/peas, digging two trenches the length of the bed for kitchen waste, shredded paper and chopped up cardboard will help retain moisture, and they should manage well enough. (Squashes would like manure ideally of course) and people do seem to grow good potatoes in sandy soil, and asparagus too. I daresay there are no spare piles of leafmould lying around?
Worms might appear once the weather warms up a bit. It mazes me where they come from: eggs lie dormant in the soil or blow about in the air, ready to hatch out when damp and warmer, so don't worry about the lack of them right now. We had very few to begin with on our second plot but 18m later things are much improved
